EXHIBIT 99.1

MKS Instruments Reports Third Quarter 2019 Financial Results

Andover, MA, October 23, 2019 — MKS Instruments, Inc. (NASDAQ: MKSI), a global provider of technologies that enable advanced processes and improve productivity, today reported third quarter 2019 financial results.

“We are very pleased with our financial results for the quarter, as we delivered sequential growth in our Semiconductor end-market, driven by strong product differentiation and execution, combined with an improving demand backdrop. Although our Advanced Markets remain constrained due to global macro-economic and trade uncertainty, we remain very excited about our product and market offerings into 2020 and beyond.” said Gerald Colella, Chief Executive Officer.

Mr. Colella added, “We are also very proud that MKS has been selected to the Fortune^® 100 Fastest-Growing Companies List for the third year in a row, ranking #21. Our strong operational and financial execution, combined with our commitment to innovation, have underpinned our ability to thrive as a global leader in the markets we serve – and we are just getting started.”

“In the quarter, we completed our tenth voluntary principal prepayment and fifth repricing of our secured term loan since loan origination in April 2016. These actions have lowered our annualized non-GAAP interest costs by almost $6 million based on current interest rates, and our goal is to continue to execute on de-levering the balance sheet. We exited the quarter with $475 million in cash and short-term investments, and $895 million of secured term loan debt,” said Seth H. Bagshaw, Senior Vice President and Chief Financial Officer.

Quarterly Consolidated Financial Results

(in millions, except per share data)

Third Quarter 2019 Financial Results

Revenue was $462.5 million, a decrease of 2% from $474.1 million in the second quarter of 2019 and a decrease of 5% from $487.2 million in the third quarter of 2018.

Net income was $47.4 million, or $0.86 per diluted share, compared to net income of $37.7 million, or $0.69 per diluted share, in the second quarter of 2019, and $93.3 million, or $1.70 per diluted share, in the third quarter of 2018.

Third quarter GAAP net income included a gain from the sale of long-lived assets of $6.8 million, acquisition and integration costs of $2.1 million associated with the acquisition of Electro Scientific Industries, Inc., or ESI, and $1.5 million of restructuring and other costs.

Non-GAAP net earnings, which exclude special charges and credits, were $61.6 million, or $1.12 per diluted share, compared to $59.9 million, or $1.09 per diluted share, in the second quarter of 2019, and $103.2 million or $1.88 per diluted share, in the third quarter of 2018.

Sales to Semiconductor customers were $223 million, an increase of 4% compared to the second quarter of 2019. Sales to Advanced Markets were $239 million, a decrease of 8% compared to the second quarter of 2019.

Additional Financial Information

The Company had $475 million in cash and short-term investments and $895 million of secured term loan debt outstanding as of September 30, 2019, which is net of a $50 million voluntary principal prepayment made during the third quarter of 2019. MKS also paid a dividend of $10.9 million or $0.20 per diluted share during the third quarter of 2019. The Company has available an unused $100 million asset-based line of credit.

Fourth Quarter 2019 Outlook

Based on current business levels, the Company expects that revenue in the fourth quarter of 2019 could range from $445 to $495 million.

At these volumes, GAAP net income could range from $0.58 to $0.91 per diluted share and non-GAAP net earnings could range from $0.85 to $1.19 per diluted share.

Conference Call Details

A conference call with management will be held on Thursday, October 24, 2019 at 8:30 a.m. (Eastern Time). To participate in the conference call, please dial (877) 212-6076 for domestic callers and (707) 287-9331 for international callers, and an operator will connect you. Participants will need to provide the operator with the Conference ID of 9980809, which has been reserved for this call. A live and archived webcast of the call will be available on the Company’s website at www.mksinst.com, along with the Company’s earnings press release and supplemental financial information.

About MKS Instruments

MKS Instruments, Inc. is a is a global provider of instruments, subsystems and process control solutions that measure, monitor, deliver, analyze, power and control critical parameters of advanced manufacturing processes to improve process performance and productivity for our customers. Our products are derived from our core competencies in pressure measurement and control, flow measurement and control, gas and vapor delivery, gas composition analysis, residual gas analysis, leak detection, control technology, ozone generation and delivery, power, reactive gas generation, vacuum technology, lasers, photonics, sub-micron positioning, vibration control, optics, and laser-based manufacturing solutions. We also provide services relating to the maintenance and repair of our products, installation services and training. Our primary served markets include semiconductor, industrial technologies, life and health sciences, and research and defense. Additional information can be found at www.mksinst.com.

Use of Non-GAAP Financial Results

This release includes measures that are not in accordance with U.S. generally accepted accounting principles (“Non-GAAP measures”). Non-GAAP measures exclude amortization of acquired intangible assets, costs associated with completed acquisitions, acquisition integration costs, fees and expenses related to our term loan, amortization of debt issuance costs, restructuring and other costs, a gain from the sale of long-lived assets, windfall tax adjustments from stock-based compensation, accrued taxes on subsidiary distributions, the tax effects of the 2017 Tax Cut and Jobs Act, deferred tax adjustments and the related tax effects of adjustments

impacting pre-tax income. These Non-GAAP measures should be viewed in addition to, and not as a substitute for, MKS’ reported results, and may be different from Non-GAAP measures used by other companies. In addition, these Non-GAAP measures are not based on any comprehensive set of accounting rules or principles. MKS management believes the presentation of these Non-GAAP measures is useful to investors for comparing prior periods and analyzing ongoing business trends and operating results.

Non-GAAP interest expense excludes amortization of debt issuance costs. On an annualized basis, GAAP interest savings, at the current interest rate, is approximately $7 million, which includes approximately $1 million of amortization of deferred financing costs.

SAFE HARBOR FOR FORWARD-LOOKING STATEMENTS

This release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 regarding the future financial performance, business prospects and growth of MKS. These statements are only predictions based on current assumptions and expectations. Actual events or results may differ materially from those in the forward-looking statements set forth herein. Among the important factors that could cause actual events to differ materially from those in the forward-looking statements are the conditions affecting the markets in which MKS operates, including the fluctuations in capital spending in the semiconductor industry and other advanced manufacturing markets, fluctuations in net sales to our major customers, the ability of MKS to successfully integrate ESI’s operations and employees, unexpected costs, charges or expenses resulting from the ESI acquisition, MKS’ ability to realize anticipated synergies and cost savings from the ESI acquisition, the terms of our term loan, competition from larger or more established companies in MKS’ markets; MKS’ ability to successfully grow ESI’s business; potential adverse reactions or changes to business relationships resulting from the ESI acquisition, the challenges, risks and costs involved with integrating the operations of the other companies we have acquired, the Company’s ability to successfully grow our business, potential fluctuations in quarterly results, dependence on new product development, rapid technological and market change, acquisition strategy, manufacturing and sourcing risks, volatility of stock price, international operations, financial risk management, and the other factors described in MKS’ most recent Annual Report on Form 10-K for the year ended December 31, 2018 and any subsequent Quarterly Reports on Form 10-Q, as filed with the SEC. MKS is under no obligation to, and expressly disclaims any obligation to, update or alter these forward-looking statements, whether as a result of new information, future events or otherwise after the date of this press release.

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Company Contact:

David Ryzhik

Vice President, Investor Relations

Telephone: (978) 557-5180

Email: david.ryzhik@mksinst.com

MKS Instruments, Inc.

Unaudited Consolidated Statements of Operations

(In thousands, except per share data)

The following supplemental Non-GAAP earnings information is presented to aid in understanding MKS’ operating results:

Note 1: Acquisition and integration costs for the three months ended September 30, 2019 and June 30, 2019, related to the acquisition of Electro Scientific Industries, Inc. (“ESI”) which closed on February 1, 2019. Acquisition and integration costs for the three months ended September 30, 2018, related to the Newport acquisition, which closed during the second quarter of 2016.

Note 2: Costs of revenues during the three months ended June 30, 2019 includes the amortization of the step-up of inventory to fair value as a result of the ESI acquisition.

Note 3: We recorded fees and expenses during the three months ended September 30, 2019, related to Amendment No. 6 which included the fifth repricing of our Secured Term Loan Credit Agreement and the combination of the two existing tranches of the Secured Term Loan Credit Agreement with a maturity date in February 2026.

Note 4: We recorded additional interest expense related to the amortization of debt issuance costs associated with our Secured Term Loan Credit Agreement.

Note 5: We recorded restructuring costs during the three months ended September 30, 2019 and June 30, 2019, which consisted primarily of severance costs related to an organization-wide reduction in workforce, the consolidation of service functions in Asia and the movement of certain products to low cost regions. Restructuring costs during the three months ended September 30, 2018 were primarily comprised of severance costs related to transferring a portion of our shared services functions to a third party as well as the consolidation of certain shared service functions in Asia.

Note 6: During the three months ended September 30, 2019, we recorded a net gain on the sale of two of our buildings in Boulder, CO and three of our buildings in Portland, OR.

Note 7: We recorded windfall tax expense (benefits) on the vesting of stock-based compensation.

Note 8: We recorded tax adjustments during the three months ended September 30, 2019 and June 30, 2019 resulting from additional guidance provided by the IRS related to 2017 tax reform.

Note 9: During the three months ended September 30, 2018, we recorded an adjustment to a tax accrual related to a planned distribution of an MKS subsidiary.

Note 10: We adjusted the transition tax on accumulated foreign earnings related to the 2017 Tax Cut and Jobs Act during the three months ended September 30, 2018.

Note 11: The Non-GAAP net earnings and Non-GAAP net earnings per diluted share amounts exclude acquisition and integration costs, the amortization of the step-up of inventory to fair value, fees and expenses related to the repricing and amendment of our Secured Term Loan Credit Agreement, amortization of debt issuance costs, restructuring and other costs, amortization of intangible assets, a gain on the sale of long-lived assets, windfall tax adjustments related to stock compensation expense, tax reform adjustments, an accrued tax on subsidiary distribution, transition tax on accumulated foreign earnings and the related tax effect of these adjustments to reflect the expected full year effective tax rate in the related period.

Note 12: The Non-GAAP income from operations and Non-GAAP operating margin exclude acquisition and integration costs, the amortization of the step-up of inventory to fair value, fees and expenses related to the repricing and amendment of our Secured Term Loan Credit Agreement, restructuring and other costs, amortization of intangible assets and a gain on the sale of long-lived assets.

Note 13: The Non-GAAP gross profit amounts and Non-GAAP gross margin exclude the amortization of the step-up of inventory to fair value related to the acquisition of ESI.

Note 14: EBITDA excludes net interest expense, income taxes, depreciation and amortization of intangible assets.

Note 15: Adjusted EBITDA excludes stock-based compensation, acquisition and integration costs, the amortization of the step-up of inventory to fair value, fees and expenses related to the repricing and amendment of our Secured Term Loan Credit Agreement, restructuring and other costs and a gain on the sale of long-lived assets.

MKS Instruments, Inc.

Unaudited Consolidated Statements of Operations

(In thousands, except per share data)

The following supplemental Non-GAAP earnings information is presented to aid in understanding MKS’ operating results:

Note 1: Acquisition and integration costs for the nine months ended September 30, 2019, related to the acquisition of Electro Scientific Industries, Inc. (“ESI”) which closed on February 1, 2019. Acquisition and integration costs for the nine months ended September 30, 2018, related to the Newport acquisition, which closed during the second quarter of 2016. During the second quarter of 2018, we reversed a portion of these costs related to severance agreement provisions that were not met.

Note 2: Costs of revenues during the nine months ended September 30, 2019 includes the amortization of the step-up of inventory to fair value as a result of the ESI acquisition.

Note 3: We recorded fees and expenses during the nine months ended September 30, 2019, related to Amendment No. 6 which included the fifth repricing of our Secured Term Loan Credit Agreement and the combination of the two existing tranches of the Secured Term Loan Credit Agreement with a maturity date in February 2026. We also recorded fees and expenses during the nine months ended September 30, 2019 related to Amendment No. 5 of our Secured Term Loan Credit Agreement. We recorded fees and expenses during the nine months ended September 30, 2018 related to the fourth repricing of our Secured Term Loan Credit Agreement.

Note 4: We recorded additional interest expense related to the amortization of debt issuance costs associated with our Secured Term Loan Credit Agreement.

Note 5: We recorded restructuring costs during the nine months ended September 30, 2019, which consisted primarily of severance costs related to an organization-wide reduction in workforce, the consolidation of service functions in Asia and the movement of certain products to low cost regions. We also recorded expense during the nine months ended September 30, 2019 related to a legal settlement from a contractual obligation we assumed as part of our acquisition of Newport Corporation. Restructuring costs during the nine months ended September 30, 2018 were primarily comprised of severance costs related to transferring a portion of our shared services functions to a third party as well as the consolidation of certain shared service functions in Asia. We also recorded environmental costs during the nine months ended September 30, 2018, related to an Environmental Protection Agency-designated Superfund site, which was acquired as part of our acquisition of Newport Corporation.

Note 6: During the nine months ended September 30, 2019, we recorded a net gain on the sale of two of our buildings in Boulder, CO and three of our buildings in Portland, OR.

Note 7: We recorded windfall tax benefits on the vesting of stock-based compensation.

Note 8: We recorded tax adjustments during the nine months ended September 30, 2019 resulting from additional guidance provided by the IRS related to 2017 tax reform.

Note 9: During the nine months ended September 30, 2018, we recorded an adjustment to a tax accrual related to a planned distribution of an MKS subsidiary.

Note 10: We adjusted the transition tax on accumulated foreign earnings related to the 2017 Tax Cut and Jobs Act during the nine months ended September 30, 2018.

Note 11: During the nine months ended September 30, 2018, we recorded a provisional deferred tax adjustment, which also includes the reversal of a tax accrual on a French dividend, related to U.S. tax reform legislation during the fourth quarter of 2017.

Note 12: The Non-GAAP net earnings and Non-GAAP net earnings per diluted share amounts exclude acquisition and integration costs, the amortization of the step-up of inventory to fair value, fees and expenses related to the repricing and amendment of our Secured Term Loan Credit Agreement, amortization of debt issuance costs, restructuring and other costs, amortization of intangible assets, a gain on the sale of long-lived assets, windfall tax benefits related to stock compensation expense, tax reform adjustments, an accrued tax on subsidiary distribution, transition tax on accumulated foreign earnings, a deferred tax adjustment and the related tax effect of these adjustments to reflect the expected full year effective tax rate in the related period.

Note 13: The Non-GAAP income from operations and Non-GAAP operating margin excludes acquisition and integration costs, the amortization of the step-up of inventory to fair value, fees and expenses related to the repricing and amendment of our Secured Term Loan Credit Agreement, restructuring and other costs, amortization of intangible assets and a gain on the sale of long-lived assets.

Note 14: The Non-GAAP gross profit amounts and Non-GAAP gross margin exclude the amortization of the step-up of inventory to fair value related to the acquisition of ESI.

Note 15: EBITDA excludes net interest expense, income taxes, depreciation and amortization of intangible assets.

Note 16: Adjusted EBITDA excludes stock-based compensation, acquisition and integration costs, the amortization of the step-up of inventory to fair value, fees and expenses related to the repricing and amendment of our Secured Term Loan Credit Agreement, restructuring and other costs, a gain on the sale of long-lived assets and other adjustments as defined in our Term Loan Credit Agreement.

MKS Instruments, Inc.

Unaudited Consolidated Balance Sheet

(In thousands)

MKS Instruments, Inc.

Unaudited Consolidated Statements of Cash Flows

(In thousands, except per share data)

MKS Instruments, Inc.

Reconciliation of GAAP Income Tax Rate to Non-GAAP Income Tax Rate

(in thousands)

MKS Instruments, Inc.

Reconciliation of GAAP Income Tax Rate to Non-GAAP Income Tax Rate

(in thousands)

MKS Instruments, Inc.

Reconciliation of GAAP Income Tax Rate to Non-GAAP Income Tax Rate

(in thousands)

Note 1: Acquisition and integration costs for the three months ended September 30, 2019 and June 30, 2019 and nine months ended September 30, 2019, related to the acquisition of Electro Scientific Industries, Inc. (“ESI”) which closed on February 1, 2019. Acquisition and integration costs for the three and nine months ended September 30, 2018, related to the Newport acquisition, which closed during the second quarter of 2016. During the second quarter of 2018, we reversed a portion of these costs related to severance agreement provisions that were not met.

Note 2: Costs of revenues during the three months ended June 30, 2019 and nine months ended September 30, 2019 includes the amortization of the step-up of inventory to fair value as a result of the ESI acquisition.

Note 3: We recorded fees and expenses during the three and nine months ended September 30, 2019, related to Amendment No. 6 which included the fifth repricing of our Secured Term Loan Credit Agreement and the combination of the two existing tranches of the Secured Term Loan Credit Agreement with a maturity date in February 2026. We also recorded fees and expenses during the nine months ended September 30, 2019 related to Amendment No. 5 of our Secured Term Loan Credit Agreement. We recorded fees and expenses during the nine months ended September 30, 2018 related to the fourth repricing of our Secured Term Loan Credit Agreement.

Note 4: We recorded additional interest expense related to the amortization of debt issuance costs associated with our Secured Term Loan Credit Agreement.

Note 5: We recorded restructuring costs during the three months ended September 30, 2019 and June 30, 2019 and the nine months ended September 30, 2019, which consisted primarily of severance costs related to an organization-wide reduction in workforce, the consolidation of service functions in Asia and the movement of certain products to low cost regions. We also recorded expense during the nine months ended September 30, 2019 related to a legal settlement from a contractual obligation we assumed as part of our acquisition of Newport Corporation. Restructuring costs during the three and nine months ended September 30, 2018 were primarily comprised of severance costs related to transferring a portion of our shared services functions to a third party as well as the consolidation of certain shared service functions in Asia. We also recorded environmental costs during the nine months ended September 30, 2018, related to an Environmental Protection Agency-designated Superfund site, which was acquired as part of our acquisition of Newport Corporation.

Note 6: During the three and nine months ended September 30, 2019, we recorded a net gain on the sale of two of our buildings in Boulder, CO and three of our buildings in Portland, OR.

Note 7: We recorded windfall tax (expense) benefits on the vesting of stock-based compensation.

Note 8: We recorded tax adjustments during the three months ended September 30, 2019, June 30, 2019 and nine months ended September 30, 2019 resulting from additional guidance provided by the IRS related to 2017 tax reform.

Note 9: During the three and nine months ended September 30, 2018, we recorded an adjustment to a tax accrual related to a planned distribution of an MKS subsidiary.

Note 10: We adjusted the transition tax on accumulated foreign earnings related to the 2017 Tax Cut and Jobs Act during the three and nine months ended September 30, 2018.

Note 11: During the nine months ended September 30, 2018, we recorded a provisional deferred tax adjustment, which also includes the reversal of a tax accrual on a French dividend, related to U.S. tax reform legislation during the fourth quarter of 2017.

MKS Instruments, Inc.

Reconciliation of Q4-19 Guidance – GAAP Net Income to Non-GAAP Net Earnings

(In thousands, except per share data)

Note 1: The Non-GAAP adjustments are tax effected at the applicable statutory rates and the difference between the GAAP and Non-GAAP tax rates.