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: Loomis Paul (VP & GM, Astex)

Holdings (Non-Derivative)

Security	Shares	Ownership
Common Stock	1861	Direct

Holdings (Derivative)

Security	Exercise Price	Expiration	Underlying	Shares	Ownership
Restricted Stock Unit	$		Common Stock (706)		Direct
Restricted Stock Unit	$		Common Stock (16225)		Direct

Footnotes

F1: 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 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, 4,225 on March 28, 2008, 3,000 on July 1, 2007 and 3,000 on March 5, 2007 grant dates.