Abstract: In a semiconductor device of the present invention, an epitaxial layer is formed on a P type single crystal silicon substrate. Isolation regions are formed in the epitaxial layer, and are divided into a plurality of element formation regions. An NPN transistor is formed in one of the element formation regions. An N type diffusion layer is formed between a P type isolation region and a P type diffusion layer which is used as a base region of the NPN transistor. This structure makes the base region and the isolation region tend not to be short-circuited. Hence, the breakdown voltage characteristics of the NPN transistor can be improved.

Abstract: In a semiconductor device of the present invention, two epitaxial layers are formed on a P type single crystal silicon substrate. One of the epitaxial layers has an impurity concentration higher than that of the other epitaxial layer. The epitaxial layers are divided into a plurality of element formation regions by isolation regions. In one of the element formation regions, an NPN transistor is formed. Moreover, between a P type diffusion layer, which is used as a base region of the NPN transistor, and a P type isolation region, an N type diffusion layer is formed. Use of this structure makes it hard for a short-circuit to occur between the base region and the isolation region. Thus, the breakdown voltage characteristics of the NPN transistor can be improved.

Abstract: In a semiconductor device according to the present invention, two epitaxial layers are formed on a P type substrate. In the substrate and the epitaxial layers, isolation regions are formed to divide the substrate and the epitaxial layers into a plurality of islands. Each of the isolation regions is formed by connecting first and second P type buried layers with a P type diffusion layer. By disposing the second P type buried layer between the first P type buried layer and the P type diffusion layer, a lateral diffusion width of the first P type buried layer is reduced. By use of this structure, a formation region of the isolation region is reduced in size.

Abstract: In the substrate and the epitaxial layer, isolation regions are formed to divide the substrate and the epitaxial layer into a plurality of element formation regions. Each of the isolation regions is formed by connecting first and second P type buried diffusion layers with a P type diffusion layer. By disposing the second P type buried diffusion layer between the first P type buried diffusion layer and the P type diffusion layer, a lateral diffusion width of the first P type buried diffusion layer is reduced. This structure allows a formation region of the isolation region to be reduced in size.

Abstract: In a semiconductor device of the present invention, two epitaxial layers are formed on a P type single crystal silicon substrate. In the epitaxial layers, P type buried diffusion layers and P type diffusion layers are formed, which form isolation regions. In this event, the P type buried diffusion layers are formed by being expanded from a surface of a first epitaxial layer. By use of this structure, lateral expansion widths of the P type buried diffusion layers are reduced. Thus, the device size of an NPN transistor can be reduced.

Abstract: In a semiconductor device of the present invention, two epitaxial layers are formed on a P type single crystal silicon substrate. One of the epitaxial layers has an impurity concentration higher than that of the other epitaxial layer. The epitaxial layers are divided into a plurality of element formation regions by isolation regions. In one of the element formation regions, an NPN transistor is formed. Moreover, between a P type diffusion layer, which is used as a base region of the NPN transistor, and a P type isolation region, an N type diffusion layer is formed. Use of this structure makes it hard for a short-circuit to occur between the base region and the isolation region. Thus, the breakdown voltage characteristics of the NPN transistor can be improved.

Abstract: In a semiconductor device of the present invention, an epitaxial layer is formed on a P type single crystal silicon substrate. Isolation regions are formed in the epitaxial layer, and are divided into a plurality of element formation regions. An NPN transistor is formed in one of the element formation regions. An N type diffusion layer is formed between a P type isolation region and a P type diffusion layer which is used as a base region of the NPN transistor. This structure makes the base region and the isolation region tend not to be short-circuited. Hence, the breakdown voltage characteristics of the NPN transistor can be improved.