Cover Page - shares	6 Months Ended
	Jul. 28, 2019	Aug. 23, 2019
Cover page.
Title of 12(b) Security	Common Stock par value $0.01 per share
Entity Address, Address Line One	200 Flynn Road
Entity Address, City or Town	Camarillo
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	93012-8790
City Area Code	805
Local Phone Number	498-2111
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Shell Company	false
Entity Small Business	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	95-2119684
Contained File Information, File Number	001-06395
Document Type	10-Q
Document Period End Date	Jul. 28, 2019
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Registrant Name	SEMTECH CORP
Entity Central Index Key	0000088941
Current Fiscal Year End Date	--01-26
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		66,530,435
Entity Emerging Growth Company	false
Trading Symbol	SMTC
Security Exchange Name	NASDAQ