Document And Entity Information - shares	3 Months Ended
	Apr. 30, 2017	May 26, 2017
Entity Information [Line Items]
Document Type	10-Q
Document Period End Date	Apr. 30, 2017
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
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		65,736,108