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<!-- DFIN New ActiveDisclosure (SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date :2023-03-14T14:41:43.7167+00:00 -->
<!-- Copyright (c) 2023 Donnelly Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="mksi_BusinessCombinationPricePerShareOfCommonStockInCash" name="BusinessCombinationPricePerShareOfCommonStockInCash" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNonCurrentAccruedCompensation" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNonCurrentAccruedCompensation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_BusinessCombinationShareReceivedPerCommonStock" name="BusinessCombinationShareReceivedPerCommonStock" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="mksi_CommonStockExercisePrice" name="CommonStockExercisePrice" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ContractWithCustomerAmountOfDeferredRevenueAndCustomerAdvancesRecognized" name="ContractWithCustomerAmountOfDeferredRevenueAndCustomerAdvancesRecognized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_ContractWithCustomerAssumedDeferredRevenueAndCustomerAdvances" name="ContractWithCustomerAssumedDeferredRevenueAndCustomerAdvances" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_ContractWithCustomerLiabilityAdditions" name="ContractWithCustomerLiabilityAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_CurrentAssetsFairValueDisclosure" name="CurrentAssetsFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DebtIssuanceCostsAmortizationPeriod" name="DebtIssuanceCostsAmortizationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_DeferredCompensationPlanAssetsFairValueDisclosure" name="DeferredCompensationPlanAssetsFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredStateLocalAndForeignIncomeTaxExpenseBenefit" name="DeferredStateLocalAndForeignIncomeTaxExpenseBenefit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxAssetsAccruedExpensesAndOtherReserves" name="DeferredTaxAssetsAccruedExpensesAndOtherReserves" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxAssetsCapitalizedResearchExpenditures" name="DeferredTaxAssetsCapitalizedResearchExpenditures" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxAssetsInterestLossAndCreditCarryforwards" name="DeferredTaxAssetsInterestLossAndCreditCarryforwards" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxAssetsInventoryAndWarrantyReserves" name="DeferredTaxAssetsInventoryAndWarrantyReserves" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxAssetsLeaseLiability" name="DeferredTaxAssetsLeaseLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxAssetsLoanCosts" name="DeferredTaxAssetsLoanCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DeferredTaxLiabilitiesDepreciationAndAmortization" name="DeferredTaxLiabilitiesDepreciationAndAmortization" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DeferredTaxLiabilitiesLoanCosts" name="DeferredTaxLiabilitiesLoanCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DeferredTaxLiabilitiesUnrealizedGainLoss" name="DeferredTaxLiabilitiesUnrealizedGainLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DeferredTaxLiabilityRightOfUseAsset" name="DeferredTaxLiabilityRightOfUseAsset" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DefinedBenefitPlanAmortizationOfActuarialGainLoss" name="DefinedBenefitPlanAmortizationOfActuarialGainLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DefinedBenefitPlanAssetsForPlanBenefitsGuaranteedRateOfReturn" name="DefinedBenefitPlanAssetsForPlanBenefitsGuaranteedRateOfReturn" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="mksi_DefinedBenefitPlanAssetsForPlanBenefitsPercentage" name="DefinedBenefitPlanAssetsForPlanBenefitsPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="mksi_DefinedBenefitPlanExpectedFutureBenefitPaymentsForNextTenYears" name="DefinedBenefitPlanExpectedFutureBenefitPaymentsForNextTenYears" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearSixToTen" name="DefinedBenefitPlanExpectedFutureBenefitPaymentsYearSixToTen" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DefinedBenefitPlanVestedBenefitObligation" name="DefinedBenefitPlanVestedBenefitObligation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_DefinedContributionPlanMinimumAnnualContributionsPerEmployeePercent" name="DefinedContributionPlanMinimumAnnualContributionsPerEmployeePercent" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_DerivativeEffectiveDates" name="DerivativeEffectiveDates" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_DerivativeNotionalAmountAtEffectiveDate" name="DerivativeNotionalAmountAtEffectiveDate" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_DerivativeTradeDates" name="DerivativeTradeDates" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_EffectiveIncomeTaxRateReconciliationChangeInIncomeTaxReserves" name="EffectiveIncomeTaxRateReconciliationChangeInIncomeTaxReserves" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_EffectiveIncomeTaxRateReconciliationExecutiveCompensation" name="EffectiveIncomeTaxRateReconciliationExecutiveCompensation" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_EffectiveIncomeTaxRateReconciliationForeignDerivedIntangibleIncome" name="EffectiveIncomeTaxRateReconciliationForeignDerivedIntangibleIncome" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_EffectiveIncomeTaxRateReconciliationWithholdingTaxesOnForeignDividendsNetOfForeignTax" name="EffectiveIncomeTaxRateReconciliationWithholdingTaxesOnForeignDividendsNetOfForeignTax" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_EmployeePerformanceAwardBonusExpense" name="EmployeePerformanceAwardBonusExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_FinanceLease" name="FinanceLease" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_FinanceLeaseCosts" name="FinanceLeaseCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_ForeignCurrencyTranslationAccumulatedImpairmentLoss" name="ForeignCurrencyTranslationAccumulatedImpairmentLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_ForeignInterestCarryforwards" name="ForeignInterestCarryforwards" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_GoodwillAcquiredDuringPeriodGross" name="GoodwillAcquiredDuringPeriodGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_GoodwillTranslationAdjustmentsGross" name="GoodwillTranslationAdjustmentsGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_IncreaseDecreaseCurrentAndNonCurrentAccruedCompensation" name="IncreaseDecreaseCurrentAndNonCurrentAccruedCompensation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_InitialCommitmentFeePercentage" name="InitialCommitmentFeePercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_InsuranceReimbursementReceived" name="InsuranceReimbursementReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_LeaseLiabilities" name="LeaseLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_LevelOfPerformanceTargetAchievedPercentage" name="LevelOfPerformanceTargetAchievedPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_LineOfCreditFacilityMinimumAdditionalBorrowingCapacity" name="LineOfCreditFacilityMinimumAdditionalBorrowingCapacity" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_LineOfCreditFacilityRenewalPeriod" name="LineOfCreditFacilityRenewalPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_MaximumPercentageOfPayrollForPurchaseOfStock" name="MaximumPercentageOfPayrollForPurchaseOfStock" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_MaximumPeriodOfCompanysResearchAndDevelopmentProjects" name="MaximumPeriodOfCompanysResearchAndDevelopmentProjects" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_MinimumAgeLimitForSpecifiedAdditionalAmount" name="MinimumAgeLimitForSpecifiedAdditionalAmount" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_MinimumPercentageOfEarningsBeforeInterestTaxesDepreciationAndAmortization" name="MinimumPercentageOfEarningsBeforeInterestTaxesDepreciationAndAmortization" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_MinimumPercentageOfRecognizedTaxBenefitsFromUncertainTaxPosition" name="MinimumPercentageOfRecognizedTaxBenefitsFromUncertainTaxPosition" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_MinimumPeriodOfCompanysResearchAndDevelopmentProjects" name="MinimumPeriodOfCompanysResearchAndDevelopmentProjects" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_NonCurrentAssetsFairValueDisclosure" name="NonCurrentAssetsFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_NonCurrentInterestRateFairValueHedgeAssetAtFairValue" name="NonCurrentInterestRateFairValueHedgeAssetAtFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_NonCurrentInterestRateFairValueHedgeLiabilitiesAtFairValue" name="NonCurrentInterestRateFairValueHedgeLiabilitiesAtFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_NonCurrentLeaseLiability" name="NonCurrentLeaseLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_NumberOfCustomersAccountedForFortySevenPercentFortyFourPercentAndThirtyThreePercentOfRevenue" name="NumberOfCustomersAccountedForFortySevenPercentFortyFourPercentAndThirtyThreePercentOfRevenue" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_NumberOfCustomersAccountedForNinetyPercentOfRevenue" name="NumberOfCustomersAccountedForNinetyPercentOfRevenue" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_NumberOfCustomersAccountedForTenOrMorePercentOfAccountsReceivable" name="NumberOfCustomersAccountedForTenOrMorePercentOfAccountsReceivable" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_NumberOfCustomersAccountedForTenOrMorePercentOfRevenue" name="NumberOfCustomersAccountedForTenOrMorePercentOfRevenue" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_NumberOfFacilitiesYetToClose" name="NumberOfFacilitiesYetToClose" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_NumberOfSharesReturnedForEachShareOfCommonStock" name="NumberOfSharesReturnedForEachShareOfCommonStock" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_OriginalIssueDiscountPercentageOfPrincipalAmount" name="OriginalIssueDiscountPercentageOfPrincipalAmount" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_OtherCurrentAssetsFairValueDisclosure" name="OtherCurrentAssetsFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_OtherCurrentLiabilitiesFairValueDisclosure" name="OtherCurrentLiabilitiesFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_OtherNonCurrentAssetsFairValueDisclosure" name="OtherNonCurrentAssetsFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_OtherNonCurrentLiabilitiesFairValueDisclosure" name="OtherNonCurrentLiabilitiesFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_PaymentsAndAdjustmentForRestructuring" name="PaymentsAndAdjustmentForRestructuring" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_PaymentsOfFinanceLeases" name="PaymentsOfFinanceLeases" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_PensionAndDeferredCompensationPlanAssets" name="PensionAndDeferredCompensationPlanAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_PercentageOfAggregateAmountOfAllCommitments" name="PercentageOfAggregateAmountOfAllCommitments" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_PercentageOfPayrollDeductionToCompensation" name="PercentageOfPayrollDeductionToCompensation" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_PrepaymentPremiumPercentageOfAggregatePrincipalAmount" name="PrepaymentPremiumPercentageOfAggregatePrincipalAmount" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ProceedsFromPaymentsForEmployeeStockAwards" name="ProceedsFromPaymentsForEmployeeStockAwards" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_RestructuringAndOtherCharges" name="RestructuringAndOtherCharges" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_RevenueRecognitionPaymentTerms" name="RevenueRecognitionPaymentTerms" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ScheduledQuarterlyPaymentsPercentageOfOriginalPrincipalAmount" name="ScheduledQuarterlyPaymentsPercentageOfOriginalPrincipalAmount" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_SegmentAssets" name="SegmentAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_SeparatelyPricedContractsTerm" name="SeparatelyPricedContractsTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareFromAcquisitionWeightedAverageGrantDateFairValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareFromAcquisitionWeightedAverageGrantDateFairValue" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesFromAcquisition" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesFromAcquisition" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPerShare" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPerShare" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodPercentageExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodPercentageExercisePrice" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPeriodDescription" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPeriodDescription" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_SignificantSupplyCommitmentTimePeriod" name="SignificantSupplyCommitmentTimePeriod" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_StockExercisePriceAsPercentageOfClosingMarketPrice" name="StockExercisePriceAsPercentageOfClosingMarketPrice" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_SupplementalRetirementBenefitsAccumulatedBenefitObligationNoncurrent" name="SupplementalRetirementBenefitsAccumulatedBenefitObligationNoncurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_SupplementalRetirementBenefitsCost" name="SupplementalRetirementBenefitsCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_TaxCreditCarryForwardExpirationYearEnd" name="TaxCreditCarryForwardExpirationYearEnd" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_TaxProvisionRelatedToHistoricalOutsideBasisDifferences" name="TaxProvisionRelatedToHistoricalOutsideBasisDifferences" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="mksi_UnderstatementOfAccumulatedOtherComprehensiveIncomeAndOtherComprehensiveIncome" name="UnderstatementOfAccumulatedOtherComprehensiveIncomeAndOtherComprehensiveIncome" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" name="UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="mksi_WarrantyPeriod" name="WarrantyPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_WeightedAverageNumberOfDilutedShares" name="WeightedAverageNumberOfDilutedShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_Investment1Domain" name="Investment1Domain" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AcquisitionDateLineItems" name="AcquisitionDateLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ChangeInContractWithCustomerLiabilityLineItems" name="ChangeInContractWithCustomerLiabilityLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_DerivativeInstrumentsGainLossNotDesignatedAsHedgingInstrumentsLineItems" name="DerivativeInstrumentsGainLossNotDesignatedAsHedgingInstrumentsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EarningsPerShareLineItems" name="EarningsPerShareLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_GoodwillAndIntangibleAssetsLineItems" name="GoodwillAndIntangibleAssetsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_IncomeTaxesLineItems" name="IncomeTaxesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_RestructuringCostAndOtherCostLineItems" name="RestructuringCostAndOtherCostLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ScheduleOfSignificantAccountingPoliciesLineItems" name="ScheduleOfSignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_StockholdersEquityLineItems" name="StockholdersEquityLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AcquisitionAndIntegrationCostMember" name="AcquisitionAndIntegrationCostMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AllowanceForSalesReturnMember" name="AllowanceForSalesReturnMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AnnualStepDownMember" name="AnnualStepDownMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AtotechLimitedMember" name="AtotechLimitedMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AtotechMember" name="AtotechMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_BacklogMember" name="BacklogMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_BaseRateBorrowingsMember" name="BaseRateBorrowingsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_BorrowingsUnderEuroTrancheBMember" name="BorrowingsUnderEuroTrancheBMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_BorrowingsUnderNewRevolvingFacilityMember" name="BorrowingsUnderNewRevolvingFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_CompletedTechnologyRightsMember" name="CompletedTechnologyRightsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_CorporateReconcilingItemsAndEliminationsMember" name="CorporateReconcilingItemsAndEliminationsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_CustomerAdvancesMember" name="CustomerAdvancesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_CustomerOneMember" name="CustomerOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_CustomerTwoMember" name="CustomerTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_DeferredRevenueMember" name="DeferredRevenueMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_DefinedBenefitPlanAssetCategoriesOtherAssetsMember" name="DefinedBenefitPlanAssetCategoriesOtherAssetsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_DevelopedTechnologyMember" name="DevelopedTechnologyMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ElectroScientificIndustriesIncMember" name="ElectroScientificIndustriesIncMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EquipmentSolutionsBusinessMember" name="EquipmentSolutionsBusinessMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EuriborRateFloorMember" name="EuriborRateFloorMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EuroChineseRenminbiMember" name="EuroChineseRenminbiMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EuroTrancheBMember" name="EuroTrancheBMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EuroTrancheMember" name="EuroTrancheMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_EuroUsDollarMember" name="EuroUsDollarMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_FederalFundsRateMember" name="FederalFundsRateMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_FederalStateAndForeignMember" name="FederalStateAndForeignMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_FirstLienNetLeverageRatioMember" name="FirstLienNetLeverageRatioMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_FurnitureAndFixturesOfficeEquipmentAndSoftwareMember" name="FurnitureAndFixturesOfficeEquipmentAndSoftwareMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_GroupInsuranceContractsMember" name="GroupInsuranceContractsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_IncrementalTermLoanFacilityMember" name="IncrementalTermLoanFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_IndefiniteMember" name="IndefiniteMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_InterestRateHedgeMember" name="InterestRateHedgeMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_IsraeliPensionAssetsMember" name="IsraeliPensionAssetsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_LaserProductsMember" name="LaserProductsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_LongTermInvestmentsMember" name="LongTermInvestmentsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_MaterialsSolutionsDivisionMember" name="MaterialsSolutionsDivisionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_MutualFundsAndExchangeTradedFundsMember" name="MutualFundsAndExchangeTradedFundsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_NewportCorporationMember" name="NewportCorporationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_NewRevolvingFacilityMember" name="NewRevolvingFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_NewTermLoanFacilityMember" name="NewTermLoanFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_NewTermLoanFacilityNetMember" name="NewTermLoanFacilityNetMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_NonLaserProductsMember" name="NonLaserProductsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OfferTerminateMember" name="OfferTerminateMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OneCustomerMember" name="OneCustomerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OperatingLossCarryforwardsExpiringTwoThousandSeventeenMember" name="OperatingLossCarryforwardsExpiringTwoThousandSeventeenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OperatingLossCarryforwardsExpiringTwoThousandThirtyNineMember" name="OperatingLossCarryforwardsExpiringTwoThousandThirtyNineMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OptionAgreementMember" name="OptionAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OriginalIssueDiscountMember" name="OriginalIssueDiscountMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_OtherCountriesMember" name="OtherCountriesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_PatentsTrademarksTradeNamesAndOtherMember" name="PatentsTrademarksTradeNamesAndOtherMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_PhotonControlIncMember" name="PhotonControlIncMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_PhotonControlMember" name="PhotonControlMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_PhotonicsSolutionsDivisionMember" name="PhotonicsSolutionsDivisionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_PriorTermLoanFacilityMember" name="PriorTermLoanFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_PriorTermLoanFacilityNetMember" name="PriorTermLoanFacilityNetMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_RestrictedStockUnitsGrantedToDirectorsMember" name="RestrictedStockUnitsGrantedToDirectorsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_RestrictedStockUnitsGrantedToEmployeesMember" name="RestrictedStockUnitsGrantedToEmployeesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SemiconductorProductsMember" name="SemiconductorProductsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_StepUpMember" name="StepUpMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_StockIncentivePlanTwoThousandFourteenMember" name="StockIncentivePlanTwoThousandFourteenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_StockIncentivePlanTwoThousandTwentyTwoMember" name="StockIncentivePlanTwoThousandTwentyTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementEightMember" name="SwapAgreementEightMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementFiveMember" name="SwapAgreementFiveMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementFourMember" name="SwapAgreementFourMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementOneMember" name="SwapAgreementOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementSevenMember" name="SwapAgreementSevenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementSixMember" name="SwapAgreementSixMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementThreeMember" name="SwapAgreementThreeMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_SwapAgreementTwoMember" name="SwapAgreementTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TermLoanMember" name="TermLoanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TermLoansUnderNewTermLoanFacilityMember" name="TermLoansUnderNewTermLoanFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TermSofrBorrowingsMember" name="TermSofrBorrowingsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TermSofrRatePlusApplicableCreditSpreadAdjustmentMember" name="TermSofrRatePlusApplicableCreditSpreadAdjustmentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TimeDepositsAndCertificatesOfDepositMember" name="TimeDepositsAndCertificatesOfDepositMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TopTenCustomersMember" name="TopTenCustomersMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_TwoThousandFourteenEmployeeStockPurchasePlanMember" name="TwoThousandFourteenEmployeeStockPurchasePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_UKPoundSterlingEuroMember" name="UKPoundSterlingEuroMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_USDollarChineseRenminbiMember" name="USDollarChineseRenminbiMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_USDollarEuroMember" name="USDollarEuroMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_USDollarJapaneseYenMember" name="USDollarJapaneseYenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_USDollarKoreanWonMember" name="USDollarKoreanWonMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_USDollarSingaporeMember" name="USDollarSingaporeMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_USDollarTaiwaneseDollarsMember" name="USDollarTaiwaneseDollarsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_UsDollarUkPoundMember" name="UsDollarUkPoundMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_UsdTrancheAMember" name="UsdTrancheAMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_UsdTrancheBMember" name="UsdTrancheBMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_VacuumSolutionsDivisionMember" name="VacuumSolutionsDivisionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_Year5Member" name="Year5Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_Years3And4Member" name="Years3And4Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ZeroCustomerMember" name="ZeroCustomerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ChangeInContractWithCustomerLiabilityTable" name="ChangeInContractWithCustomerLiabilityTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_DerivativeAndHedgingTable" name="DerivativeAndHedgingTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_GoodwillAndIntangibleAssetsTable" name="GoodwillAndIntangibleAssetsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_IncomeTaxesTableTable" name="IncomeTaxesTableTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ScheduleOfEarningsPerShareTable" name="ScheduleOfEarningsPerShareTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ScheduleOfRestructuringAndOtherCostTable" name="ScheduleOfRestructuringAndOtherCostTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_ScheduleOfSignificantAccountingPoliciesTable" name="ScheduleOfSignificantAccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_StockholdersEquityTable" name="StockholdersEquityTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="mksi_AccountsReceivableAllowancesPolicyTextBlock" name="AccountsReceivableAllowancesPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_CashAndCashEquivalentsAndInvestmentsPolicyTextBlock" name="CashAndCashEquivalentsAndInvestmentsPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ExpenseOfRestructuringActivitiesAndOtherTextBlock" name="ExpenseOfRestructuringActivitiesAndOtherTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ScheduleOfAllocationOfPurchasePriceTableTextBlock" name="ScheduleOfAllocationOfPurchasePriceTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ScheduleOfBusinessCombinationAcquireeNetRevenuesAndNetEarningsTableTextBlock" name="ScheduleOfBusinessCombinationAcquireeNetRevenuesAndNetEarningsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ScheduleOfCapitalExpenditureDepreciationAndAmortizationAndAssetsReportableSegmentsTableTextBlock" name="ScheduleOfCapitalExpenditureDepreciationAndAmortizationAndAssetsReportableSegmentsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_ScheduleOfFutureLeasePaymentsUnderNonCancelableLeasesTableTextBlock" name="ScheduleOfFutureLeasePaymentsUnderNonCancelableLeasesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="mksi_SummaryOfWeightedAverageRemainingTermsForAllLeasesTableTextBlock" name="SummaryOfWeightedAverageRemainingTermsForAllLeasesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
</xsd:schema>
