MKS INC — Director's Dealing 2011

May 3, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2011-05-02

Reporting Person: CHUTE RICHARD S (Director)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2011-05-02	Common Stock	A	6000	—	Acquired	13000	Direct
2011-05-02	Common Stock	S	6000	$28.323	Disposed	7000	Direct

Footnotes

F1: This RSU grant fully vests on the day prior to the first annual meeting of shareholders following the date of grant (or if no such meeting is held within 13 months after the date of grant, on the 13 month anniversary of the date of grant).

F2: Each restricted stock unit represents the contingent right to receive one share of common stock of MKS Instruments, Inc.

F3: This transaction was executed in multiple trades at prices ranging from $28.119 to $28.43 The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide, upon request, the full information regarding the number of shares and prices at which the transaction was effected.