(MKS LOGO)

EXHIBIT 99.1

Contact: Seth H. Bagshaw
Vice President, Chief Financial Officer & Treasurer
Telephone: 978.645.5578

MKS Instruments Reports Q2 2011 Financial Results
Record Non-GAAP net earnings of $38.8 million; up 16% from Q2 of 2010

Andover, Mass., July 20, 2011 — MKS Instruments, Inc. (NASDAQ: MKSI), a global provider of technologies that enable advanced processes and improve productivity; today reports second quarter 2011 financial results.

Second Quarter Financial Results

Sales were $224.5 million, up 2% from $220.6 million in the second quarter of 2010 and down 3% from a record $231.9 million in the first quarter of 2011.

Second quarter net income was $38.6 million, or $0.73 per diluted share, compared to net income of $38.8 million, or $0.76 per diluted share, in the second quarter of 2010 and $38.0 million, or $0.73 per diluted share, in the first quarter of 2011.

Record Non-GAAP net earnings were $38.8 million, or $0.73 per diluted share, compared to $33.4 million, or $0.66 per diluted share, in the second quarter of 2010 and $38.2 million, or $0.73 per diluted share, in the first quarter of 2011.

Also in the second quarter, the board of directors authorized a quarterly cash dividend of $0.15 per share which was paid on June 17th. Cash and investments, net of short-term borrowings, were $500.9 million at the end of the quarter, while stockholders’ equity, net of intangible assets and goodwill, was $807.7 million at quarter end.

Leo Berlinghieri, Chief Executive Officer and President, said, “We are pleased to report another strong quarter for MKS, with continued strength in the semiconductor market being somewhat offset by a decline in solar business following our record shipments in Q1. Our operating leverage further improved with favorable product mix coupled with effective cost controls. After a robust first half of the year, we are seeing some softening in the semiconductor market as the record shipments of the last few quarters are assimilated and brought on line. We expect that the solar market will remain slightly depressed in the third quarter, but we anticipate that sales to our other markets should continue to remain strong. Based upon these patterns and general business outlook, we estimate that our third quarter sales may range from $180 to $210 million and at this volume, our non-GAAP net earnings could range from $0.40 to $0.60 per share.”

Conference Call Details

A conference call with management will be held on Thursday, July 21, 2011 at 8:30 a.m. (Eastern Time). To participate in the conference call, please dial (877) 666-7169 for domestic callers and (817) 382-5829 for international callers, and an operator will connect you. Participants will need to provide the operator with the Conference ID of 82212141, which has been reserved for this call. A live and archived webcast of the call will also be available on the company’s website at www.mksinst.com. Following the webcast, a telephone replay will be available for 7 days. To access the replay, please dial (800) 642-1687 or (706) 645-9291 which will require the conference ID noted above.

Use of Non-GAAP Financial Results

Non-GAAP net earnings and Non-GAAP net earnings per share amounts which exclude discontinued operations, amortization of acquired intangible assets, costs associated with acquisitions and disposition related charges, are not in accordance with Accounting Principles Generally Accepted in the United States of America (GAAP). MKS’ management believes the presentation of these non-GAAP financial measures, which exclude discontinued operations, amortization of acquired intangible assets, costs associated with acquisitions and disposition related charges, is useful to investors for comparing prior periods and analyzing ongoing business trends and operating results.

About MKS Instruments

MKS Instruments, Inc. is a global provider of instruments, subsystems and process control solutions that measure, control, power, monitor and analyze critical parameters of advanced manufacturing processes to improve process performance and productivity. Our products are derived from our core competencies in pressure measurement and control, materials delivery, gas composition analysis, control and information technology, power and reactive gas generation, and vacuum technology. Our primary served markets are manufacturers of capital equipment for semiconductor devices, and for other thin film applications including flat panel displays, solar cells, light emitting diodes, data storage media, and other advanced coatings. We also leverage our technology in other markets with advanced manufacturing applications including medical equipment, pharmaceutical manufacturing, energy generation, and environmental monitoring.

Forward-Looking Statements

This release contains projections or other forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27 of the Securities Act, and Section 21E of the Securities Exchange Act regarding MKS’ future growth and the future financial performance of MKS. These projections or statements are only predictions. Actual events or results may differ materially from those in the projections or other forward-looking statements set forth herein. Among the important factors that could cause actual events to differ materially from those in the projections or other forward-looking statements are the fluctuations in capital spending in the semiconductor industry, fluctuations in net sales to MKS’ major customers, potential fluctuations in quarterly results, the challenges, risks and costs involved with integrating the operations of MKS and any acquired companies, 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 future growth subject to risks. Readers are referred to MKS’ filings with the Securities and Exchange Commission, including its most recent Annual Report on Form 10-K and Quarterly Reports on Form 10-Q, for a discussion of these and other important risk factors concerning MKS and its operations. MKS is under no obligation to, and expressly disclaims any obligation to, update or alter its forward-looking statements, whether as a result of new information, future events or otherwise.

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MKS Instruments, Inc.
Unaudited Consolidated Statements of Operations
(In thousands, except per share data)

Note 1: During 2010, the Company sold two product lines that no longer met the Company’s long-term strategic objectives. The results of operations of the two product lines have been classified as discontinued operations in the consolidated statements of operations for all periods presented.

Note 2: The Non-GAAP net earnings and Non-GAAP net earnings per share amounts exclude results of discontinued operations, amortization of acquired intangible assets, acquisition and disposition related charges, net of applicable income taxes.

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MKS Instruments, Inc.
Unaudited Consolidated Statements of Operations
(In thousands, except per share data)

Note 1: During 2010, the Company sold two product lines that no longer met the Company’s long-term strategic objectives. The results of operations of the two product lines have been classified as discontinued operations in the consolidated statements of operations for all periods presented.

Note 2: The six month period ended June 30, 2010 includes a $682 gain on the sale of a vacated facility.

Note 3: The Non-GAAP net earnings and Non-GAAP net earnings per share amounts exclude results of discontinued operations, amortization of acquired intangible assets, acquisition and disposition related charges, net of applicable income taxes.

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MKS Instruments, Inc.
Unaudited Consolidated Balance Sheet
(In thousands)

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