Abstract: A semiconductor device includes a trench extending from a surface of a P-base layer to a surface of a P-well layer. The trench has a trench end portion defined in the surface of the P-well layer and in a direction in which the trench extends. The trench has first and second regions. The first region extends from the trench end portion to get into the surface of the P-base layer near a boundary between the P-base layer and the P-well layer. The second region extends in the surface of the P-base layer from an end portion of the first region. A trench width is greater in the first region than in the second region.

Abstract: A semiconductor device includes a trench extending from a surface of a P-base layer to a surface of a P-well layer. The trench has a trench end portion defined in the surface of the P-well layer and in a direction in which the trench extends. The trench has first and second regions. The first region extends from the trench end portion to get into the surface of the P-base layer near a boundary between the P-base layer and the P-well layer. The second region extends in the surface of the P-base layer from an end portion of the first region. A trench width is greater in the first region than in the second 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.

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.