Abstract: An element separating oxide film is formed in a surface of a p-type silicon substrate for separation of an element forming region. A p-type impurity diffusion region extends from the vicinity of a lower surface of the element separating oxide film to a position at a predetermined depth in the element forming region. The p-type impurity diffusion region has a peak of concentration of impurity. In the element forming region adjacent to the element separating oxide film, an n.sup.+ impurity diffusion region is formed on the surface of the p-type silicon substrate. An n.sup.- impurity diffusion region adjacent to the n.sup.+ impurity diffusion region is formed between the n.sup.+ impurity diffusion region and the p-type impurity diffusion region.

Abstract: An element separating oxide film is formed in a surface of a p-type silicon substrate for separation of an element forming region. A p-type impurity diffusion region extends from the vicinity of a lower surface of the element separating oxide film to a position at a predetermined depth in the element forming region. The p-type impurity diffusion region has a peak of concentration of impurity. In the element forming region adjacent to the element separating oxide film, an n.sup.+ impurity diffusion region is formed on the surface of the p-type silicon substrate. An n.sup.- impurity diffusion region adjacent to the n.sup.+ impurity diffusion region is formed between the n.sup.+ impurity diffusion region and the p-type impurity diffusion region.