Patent ID: 7960796

Claim:
A semiconductor device comprising: a substrate of a first conductivity type; an epitaxial layer of a second conductivity type formed on said substrate; a buried diffusion layer of the second conductivity type formed in an upper surface layer of a prescribed area of said substrate and formed in an under surface of said epitaxial layer on the prescribed area of the substrate; a high-concentration diffusion layer of the first conductivity type formed directly on said, buried diffusion layer of the second conductivity type; a first high-concentration isolation diffusion layer of the first conductivity type formed in the upper surface layer of an area of said substrate and formed in the under surface of said epitaxial layer on the area of said substrate so as to surround said buried diffusion layer, and said first high-concentration isolation diffusion layer is in both the epitaxial layer and the substrate; a second high-concentration isolation diffusion layer of the first conductivity type formed in said epitaxial layer on said first high-concentration isolation diffusion layer; a p-type well region formed on said high-concentration diffusion layer; an n-type well region formed on said buried diffusion layer adjacent said p-type well region; and a low-concentration isolation diffusion layer of the first conductivity type formed on said second high-concentration isolation diffusion layer, for isolating said epitaxial layer into a plurality of island regions, wherein one each of immediately adjacent said first high-concentration isolation diffusion layer, second high-concentration isolation diffusion layer, and low-concentration isolation diffusion layer form a first isolation diffusion region, another one each of immediately adjacent said first high-concentration isolation diffusion layer, second high-concentration isolation diffusion layer, and low-concentration isolation diffusion layer form a second isolation diffusion region, one of said plurality of island regions is located between said p-type well region and said first isolation diffusion region, another one of said plurality of island regions is located between said n-type well region and said second isolation diffusion region, and as seen in a cross-sectional view only said one of said plurality of island regions is between said p-type well region and said first isolation diffusion region along a straight line extending from said p-type well region to said first isolation diffusion region, and only said another one of said plurality of island regions is between said n-type well region and said second isolation diffusion region along a straight line extending from said n-type well region to said second isolation diffusion region.