Patent ID: 8507945

Claim:
A semiconductor device comprising: a semiconductor substrate having a first main surface and a second main surface facing each other; an element having a gate electrode formed on a side of said first main surface, a first electrode formed on the side of said first main surface and a second electrode formed in contact with said second main surface, said element generating an electric field in a channel by a voltage applied to said gate electrode, and controlling a current between said first electrode and said second electrode by the electric field in said channel; and a collector region formed on said second main surface, said collector region including a collector diffusion layer of a first conductivity type in contact with said second electrode, and a buffer diffusion layer of a second conductivity type formed closer to the first main surface than said collector diffusion layer is, wherein an impurity concentration of said collector diffusion layer in an interface between said second electrode and said collector diffusion layer is not less than 5.0×10 15 cm −3 and not more than 1.0×10 22 cm −3 .