Patent ID: 8723253

Claim:
A semiconductor transistor device, comprising: a first semiconductor layer of a first conductivity type; a plurality of base regions of a second conductivity type, the base regions provided on a surface of the first semiconductor layer; a source region of the first conductivity type selectively provided on each of surfaces of the base regions; a first major electrode electrically connected to the first semiconductor layer; a second major electrode electrically connected to the source region; a gate electrode provided via a gate insulating film in each of a pair of trenches on a side of the second major electrode, each of the trenches reaching from a surface of the source region to the first semiconductor layer; and a field plate electrode provided via a field plate insulating film in each of the pair of trenches on a side of the first major electrode, a thickness of a part of the field plate insulating film being greater than a thickness of the gate insulating film, an interface between the first semiconductor layer and the part of the field plate insulating film, not being provided between the source region and the first major electrode, and being provided between the base region and the first major electrode in a direction in which each of the pair of trenches are aligned, a width of the first semiconductor layer between the pair of trenches at a position of a part of the field plate insulating film being narrower than a width of each of the base regions between the pair of trenches at a position of the gate insulating film, and the source region not being formed directly above the interface between the first semiconductor layer and the part of the field plate insulating film.