Document And Entity Information - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Jan. 29, 2017	Mar. 17, 2017	Jan. 27, 2017	Jul. 31, 2016
Entity Information [Line Items]
Document Type	10-K
Document Period End Date	Jan. 29, 2017
Amendment Flag	false
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Entity Registrant Name	SEMTECH CORP
Entity Central Index Key	0000088941
Current Fiscal Year End Date	--01-29
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		65,973,747
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Public Float				$ 1,100
Share Price			$ 33.70	$ 25.42