Patent ID: 8563987

Claim:
A semiconductor device comprising: a substrate; a semiconductor layer which is arranged on the principal surface of the substrate and which is made of a wide bandgap semiconductor; a trench which is arranged in the semiconductor layer and which has a bottom and a side surface; an insulating region which is arranged on the bottom and side surface of the trench; and a conductive layer which is arranged in the trench and which is insulated from the semiconductor layer by the insulating region, wherein the insulating region includes a gate insulating film that is arranged on the bottom and the side surface of the trench and a gap that is arranged between the gate insulating film and the conductive layer at the bottom of the trench, and wherein the gate insulating film contacts with the conductive layer on a portion of the side surface of the trench but does not contact with the conductive layer at the bottom of the trench, and wherein the thickness of the insulating region as measured from the bottom of the trench through the lower surface of the conductive layer is greater around the center of the trench than beside the side surface of the trench.