MKS INC — Director's Dealing 2011

Mar 18, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2011-03-16

Reporting Person: Lee John Tseng-Chung (Group VP)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2011-03-16	Common Stock	M	2042	—	Acquired	4276.147	Direct
2011-03-16	Common Stock	M	1458	—	Acquired	5734.147	Direct
2011-03-16	Common Stock	F	1285	$28.51	Disposed	4449.147	Direct
2011-03-17	Common Stock	S	4449	$29.306	Disposed	0.147	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2011-03-16	Restricted Stock Unit	$	M	2042	Disposed		Common Stock (2042)	Direct
2011-03-16	Restricted Stock Unit	$	M	1458	Disposed		Common Stock (1458)	Direct

Footnotes

F1: Each restricted stock unit represents the contingent right to receive one share of common stock of MKS Instruments, Inc.

F2: This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person.

F3: This transaction was executed in multiple trades at prices ranging from $29.29 to $29.35 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.

F4: These RSUs are subject to the achievement of performance criteria determined in the first year of the grant and thereafter vests in equal annual installments over three years.

F5: The RSUs vest in equal annual installments over three years.