A semiconductor device includes a heterojunction semiconductor region 9, which forms a heterojunction with a drain region 2. The heterojunction semiconductor region 9 is connected to a source electrode 7, and has a band gap different from a band gap of a semiconductor substrate constituting the drain region 2. It is possible to set the size of an energy barrier against conduction electrons, which is formed between the drain region 2 and the heterojunction semiconductor region 9, into a desired size by changing the conductivity type or the impurity density of the heterojunction semiconductor region 9. This is a characteristic not found in a Schottky junction, in which the size of the energy barrier is inherently determined by a work function of a metal material. It is easy to achieve optimal design of a passive element in response to a withstand voltage system of a MOSFET as a switching element. It is also possible to suppress diffusion potential in a reverse conduction mode and to improve a degree of integration per unit area. As a result, it is possible to reduce the size of elements and to simplify manufacturing processes thereof.