A semiconductor device for a charge pump device suitable for providing large current capacity and preventing a latch up from occurring is offered. An N-type epitaxial silicon layer is formed on a P-type single crystalline silicon substrate, and a P-type well region is formed in the N-type epitaxial silicon layer. A P+-type buried layer abutting on a bottom of the P-type well region and an N+-type buried layer partially overlapping with the P+-type buried layer and electrically isolating the P-type well region from the single crystalline silicon substrate are formed. And then, an MOS transistor is formed in the P-type well region.