Patent ID: 7368783

Claim:
A semiconductor device comprising: a semiconductor substrate having a first major surface and a second major surface; a lightly-doped semiconductor layer of a first conductivity type, formed on the first major surface of the semiconductor substrate; an active region formed on a top of an island-shaped region on a surface of the lightly-doped semiconductor layer, the active region including a first semiconductor region of a second conductivity type formed on the lightly-doped semiconductor layer, and a second semiconductor region of the first conductivity type formed on the first semiconductor region; a first electrode surrounding the active region and extending toward the lightly-doped semiconductor layer to a deeper position than the active region; a first insulating film formed at least between a side surface of the active region and the first electrode; a buried field relaxation layer formed in the lightly-doped semiconductor layer adjacent to a bottom surface of the first electrode, the buried field relaxation layer including a first field relaxation layer of the second conductivity type and second field relaxation layers of the first conductivity type formed at two ends of the first field relaxation layer; a second electrode formed on the second semiconductor region on the first major surface; and a third electrode formed on the second major surface.