Semiconductor device with high withstand voltage and a drain layer having a highly conductive region connectable to a diffused source layer by an inverted layer

Abstract

A highly conductive region serving as a surface of a drain layer of a first conductivity type is diffused more deeply than a main diffused layer and a diffused channel layer and has a small conducting resistance. The highly conductive region is surrounded by a diffused region of a second conductivity type which comprises a diffused base layer and a diffused guard ring layer Therefore, the highly conductive region does not form spherical junctions, and a depletion layer spreading in the highly conductive region extends into the highly conductive region The highly conductive region thus has a high withstand voltage while maintaining the low conducting resistance.