X0306 4 2017-12-14 0001049502 MKS INSTRUMENTS INC MKSI 0001256715 COLELLA GERARD G 2 TECH DRIVE ANDOVER MA 01810 1 1 CEO, President, Director Common Stock 2017-12-14 4 S 0 5000 95.26 D 56296 I By Gerald G. Colella Living Trust Common Stock 5024.65 D This transaction was executed in multiple trades at prices ranging from $95.200 to $95.350. 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. /s/ M. Kathryn Rickards, attorney-in-fact 2017-12-15