Abstract: A high voltage semiconductor device is provided and includes an n?-type region encompassed by a p? well region and is provided on a p?-type silicon substrate. A drain n+-region is connected to a drain electrode. A p base region is formed so as to be separate from and encompass the drain n+-region. A source n+-region is formed in the p base region. Further, a p?-region is provided that passes through the n?-type region to the silicon substrate. The n?-type region is divided, by the p?-region, into a drift n?-type region having the drain n+-region and a floating n?-type region having a floating electric potential.