A semiconductor device according to the present invention includes: a semiconductor layer; an element separating portion, formed in a top layer portion of the semiconductor layer and separating, in the semiconductor layer, a first element forming region for forming a first conductive type MOSFET and a second element forming region for forming a second conductive type MOSFET; a first gate insulating film, selectively formed on a top surface of the semiconductor layer in the first element forming region; a first gate electrode, formed on the first gate insulating film; a first sidewall, formed at a periphery of the first gate insulating film and the first gate electrode; a second gate insulating film, selectively formed on a top surface of the semiconductor layer in the second element forming region; a second gate electrode, formed on the second gate insulating film; and a second sidewall, formed at a periphery of the second gate insulating film and the second gate electrode. The first sidewall includes: a base, contacting the top surface of the semiconductor layer; and a main body, formed on the base and protruding laterally beyond a peripheral edge of the base.