Patent ID: 7049657

Claim:
A semiconductor device comprising: a first semiconductor layer of a first conductivity type; a second semiconductor layer of a second conductivity type provided on the first semiconductor layer; a trench penetrating the second semiconductor layer and intruding into the first semiconductor layer; a thick gate insulating film provided on a inner wall of the trench below an upper surface of the first semiconductor layer; a thin gate insulating film provided on the inner wall of the trench at a part upper than the thick gate insulating film; a gate electrode filling the trench; and a semiconductor region of a second conductivity type selectively formed to adjoin the trench and to project from a bottom surface of the second semiconductor layer into the first semiconductor layer, a lower end of a part of the semiconductor region of the second conductivity type in contact with the trench being substantially at a same level as a boundary between the thick gate insulating film and the thin gate insulating film, and a carrier concentration of the semiconductor region of the second conductivity type being higher than a carrier concentration of the first semiconductor layer and lower than a carrier concentration of the second semiconductor layer.