Semiconductor device

Claim 1

An integrated semiconductor circuit having a drive circuit and a conductivity modulated MOS output transistor which has a high resistance layer whose conductivity can be modulated comprising: a P type semiconductor substrate having a main surface and a back surface; an N type semiconductor layer formed directly on said main surface of said P type semiconductor substrate and having an outer surface; an isolation region extending from said outer surface of the semiconductor layer to said P type semiconductor substrate to separate said semiconductor layer into first and second device forming regions; a drive circuit device formed in said first device forming region; at least one P type semiconductor region formed in the surface area of said second device forming region; an N type semiconductor region formed in each said P type semiconductor region; an insulation layer formed on at least a portion of each said P type semiconductor region which lies between said second device forming region and said N type semiconductor region; a gate electrode formed on said insulation layer; and a drain electrode formed on said back surface of said P type semiconductor substrate; wherein said gate electrode, said P type and N type semiconductor regions, said second device forming region, and said P type semiconductor substrate form a vertically disposed conductivity modulated MOS transistor through which a current flows from said P type semiconductor substrate to said N type semiconductor region through said N type semiconductor layer and said P type semiconductor region in said second device forming region, said MOS transistor having a high resistance layer whose conductivity can be modulated and which constitutes an output circuit, and wherein holes injected from said P type semiconductor substrate into said N type semiconductor layer through a PN junction formed therebetween serve to increase the conductivity of said high resistance layer during operation of the circuit.