A semiconductor device includes: a first-conductivity-type semiconductor substrate serving as a drain layer; a first-conductivity-type epitaxial layer formed on the semiconductor substrate; a first-conductivity-type source layer formed in a surface part of the epitaxial layer; two second-conductivity-type gate layers formed in the surface part of the epitaxial layer so as to sandwich the source layer; a first-conductivity-type channel forming layer formed so as to be sandwiched between the two gate layers, the first-conductivity-type channel forming layer being formed on an inner side of the source layer in the epitaxial layer; and an electrode connected to one of the drain layer, the source layer, and the gate layer. In the channel forming layer, two first-conductivity-type impurity layers each having a substantially predetermined width are formed adjacent to each other in a direction crossing a channel.