Patent ID: 7602025

Claim:
A high voltage semiconductor device comprising: a semiconductor layer of a first conductivity type joined to a semiconductor substrate via an insulating film; a drift diffusion layer of a second conductivity type formed in a predetermined region in said semiconductor layer of the first conductivity type; a base diffusion layer of the first conductivity type formed in said semiconductor layer of the first conductivity type apart from said drift diffusion layer of the second conductivity type; an emitter diffusion layer of the second conductivity type formed in said base diffusion layer of the first conductivity type; a collector buffer layer of the second conductivity type formed in said semiconductor layer of the first conductivity type on the opposite side of said base diffusion layer of the first conductivity type across said drift diffusion layer of the second conductivity type; a collector diffusion layer of the first conductivity type formed in said collector buffer layer of the second conductivity type; a gate electrode formed on said base diffusion layer of the first conductivity type at least between said emitter diffusion layer of the second conductivity type and said drift diffusion layer of the second conductivity type via a gate insulating film; and a field insulating film formed on said drift diffusion layer of the second conductivity type; wherein said drift diffusion layer of the second conductivity type is formed so as to surround said collector buffer layer of the second conductivity type; in a straight-line portion, which is an end portion of said collector diffusion layer of the first conductivity type in a potential transferring direction, an impurity of the second conductivity type is diffused from both of the ends to form a first overlapped region in the center, and a second overlapped region where said drift diffusion layer of the second conductivity type overlaps said collector buffer layer of the second conductivity type.