A semiconductor device is disclosed, which comprises a semiconductor substrate, source/drain regions formed in the semiconductor substrate, a gate insulating film formed on a channel region between the source/drain regions, a gate electrode formed on the gate insulating film, and a sidewall insulating film formed on a sidewall surface of the gate electrode, wherein the gate electrode is made of SiGe, the sidewall insulating film is an insulating film obtained by oxidizing the sidewall surface of the gate electrode, and the sidewall insulating film contains silicon oxide as a main component.