A semiconductor device according to the present invention includes a silicon substrate having a main surface, a gate electrode provided on the main surface of the silicon substrate, a first sidewall insulating film provided to cover a side surface of the gate electrode and including two layers of an oxide sidewall film as an underlay and a nitride sidewall film, a second sidewall insulating film provided to cover a surface of the first sidewall insulating film, and a cobalt silicide layer arranged above source and drain regions and at a position farther than the second sidewall insulating film from the gate electrode. The second sidewall insulating film fills in a removed portion located at a lower end of the oxide sidewall film. This allows a semiconductor device formed by employing a salicide process to prevent increase of leak current caused by a metal silicide layer.