A DMOS type semiconductor device and a method for manufacturing the same are provided. An isolation oxide layer with an ion implantation opening is formed on a semiconductor. A gate oxide film is formed on the semiconductor within the ion implantation opening. A gate is formed on the isolation oxide layer and the gate oxide film. A body layer diffusively formed in the semiconductor by implanting ions of an impurity element having a first conduction type from the ion implantation opening. A regulation layer which is shallower than the body layer is diffusively formed in the body layer by implanting ions of an impurity element having a second conduction type opposite to the first conduction type from the ion implantation opening. A source layer is diffusively formed in the regulation layer by implanting ions of an impurity element having the second conduction type from the ion implantation opening. The regulation layer is formed so as to horizontally extend beyond a region in which a gate bird's beak occurs from an end of the gate toward underlying layers of the gate.