A semiconductor device provided with a MIS type field effect transistor comprising a silicon substrate, a gate insulating film having a high-dielectric-constant metal oxide film which is formed on the silicon substrate via a silicon containing insulating film, a silicon-containing gate electrode formed on the gate insulating film, and a sidewall including, as a constituting material, silicon oxide on a lateral face side of the gate electrode, wherein a silicon nitride film is interposed between the sidewall and at least the lateral face of the gate electrode. This semiconductor device, although having a fine structure with a small gate length, is capable of low power consumption and fast operation.