MKS INC — Director's Dealing 2010

May 11, 2010

SEC Form 3 — Initial Statement of Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2010-05-03

Reporting Person: Eyerman Paul (VP & GM, ENI and Medical)

Holdings (Non-Derivative)

Security	Shares	Ownership
Common Stock	100	Direct

Holdings (Derivative)

Security	Exercise Price	Expiration	Underlying	Shares	Ownership
Restricted Stock Unit	$		Common Stock (2647)		Direct
Restricted Stock Unit	$		Common Stock (13250)		Direct

Footnotes

F1: The RSUs vest in one year from the August 28, 2009 grant date.

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

F3: The RSUs vest in 3 years after grant date (broken out by amount and corresponding grant date as follows: 5,000 on April 9, 2010, 4,000 on May 26, 2009, 4,250 on March 28, 2008 and 5,000 on March 5, 2007).