Patent ID: 8507982

Claim:
A semiconductor device comprising: a drift diffusion region of a first conductivity type formed in an upper portion of a semiconductor substrate; a body diffusion region of a second conductivity type formed in an upper portion of the drift diffusion region; a source diffusion region of the first conductivity type formed in an upper portion of the body diffusion region; an insulating film buried in a trench formed in an upper portion of the drift diffusion region, and spaced apart from the body diffusion region; a drain diffusion region of the first conductivity type formed in an upper portion of the drift diffusion region and adjacent to the insulating film on an opposite side of the insulating film from the source diffusion region; and a gate electrode formed on a portion of the body diffusion region, the drift diffusion region, and a portion of the insulating film with a gate insulating film being interposed between the gate electrode, and the portion of the body diffusion region, the drift diffusion region, and the portion of the insulating film, wherein the drift diffusion region includes both a substrate inner region and a surface region, said surface region directly contacts the body diffusion region, the surface region is formed between the substrate inner region and the gate electrode, and the surface region contains an impurity of the first conductivity type at a higher concentration than that of the substrate inner region.