Patent ID: 8129779

Claim:
A semiconductor device comprising: a semiconductor layer; a first conductivity type region of a first conductivity type formed on a base layer portion of the semiconductor layer; a body region of a second conductivity type formed on the semiconductor layer to be in contact with the first conductivity type region; a trench formed on the semiconductor layer to penetrate through the body region so that a deepest portion thereof reaches the first conductivity type region; a source region of the first conductivity type formed on a surface layer portion of the semiconductor layer around the trench to be in contact with the body region; a gate insulating film formed on a bottom surface and a side surface of the trench; a gate electrode embedded in the trench through the gate insulating film; a gate plug provided on the gate electrode; and a source plug provided on the source region, the source plug insulated from the gate plug by an insulation film, wherein the gate insulating film is so formed that the thickness of a first portion in direct contact with the source region is larger than the thickness of a second portion in contact with the body region on the side surface of the trench, and the first portion projects both inwardly and outwardly relative to the trench with respect to the second portion to have the thickness larger than the thickness of the second portion.