Document And Entity Information - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Jan. 28, 2018	Mar. 16, 2018	Jan. 26, 2018	Jul. 30, 2017
Entity Information [Line Items]
Document Type	10-K
Document Period End Date	Jan. 28, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Registrant Name	SEMTECH CORP
Entity Central Index Key	0000088941
Current Fiscal Year End Date	--01-28
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		66,521,122
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Public Float				$ 2,000
Share Price			$ 36.45	$ 39.75