Patent ID: 7871888

Claim:
A method of forming a semiconductor of a MOSFET or IGBT, comprising the steps of: forming a RESURF region of a second-conductivity type in one surface of a semiconductor layer of a first-conductivity type, wherein the RESURF region has an annular configuration; forming a plurality of trenches from the one surface of the semiconductor layer after forming the RESURF region, wherein each of the trenches has a striped configuration and a depth smaller than a diffusion depth of the RESURF region, and wherein the RESURF region surrounds the trenches with opposite longitudinal ends of each of the trenches overlapping portions of the RESURF region; forming trench gate electrodes in the trenches with a first insulating film interposed between each of the trench gate electrodes and the trenches after forming the trenches; forming a well region of the second-conductivity type in the one surface of the semiconductor layer, wherein the well region intersects the RESURF region.