Document And Entity Information (USD $) In Billions, except Share data, unless otherwise specified	12 Months Ended
	Jan. 29, 2012	Mar. 22, 2012	Jul. 29, 2011
Document And Entity Information [Abstract]
Document Type	10-K
Document Period End Date	Jan. 29, 2012
Amendment Flag	false
Document Fiscal Year Focus	2012
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		65,406,752
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 1.23