A method for producing a semiconductor device of a type in which carriers are passed between a drain electrode and a source electrode by means of a tunnel current which is controlled by a voltage applied to a gate electrode and which flows between the drain electrode and the source electrode via a drive point, the semiconductor device including: a semiconductor substrate (1, 2) made of at least one selected from the group consisting of silicon carbide, gallium nitride and diamond, a semiconductor region made of at least one selected from the group consisting of single crystal silicon, polycrystal silicon, amorphous silicon, germanium and gallium arsenide, said semiconductor region being configured to contact a first main face of the semiconductor substrate (1, 2) and different from the semiconductor substrate (1, 2) in band gap, the gate electrode contacting, via a gate insulating film made of silicon dioxide, a part of a junction part between the semiconductor region and the semiconductor substrate (1, 2), the source electrode configured to connect with the semiconductor region, and the drain electrode configured to make an ohmic connection with the semiconductor substrate (1, 2), the method comprising the following sequential operations: forming the semiconductor region on the first main face of the semiconductor substrate (1, 2); etching a part of the semiconductor region; and forming the gate insulating film both on the semiconductor region that is etched and the semiconductor substrate (1, 2) that is exposed after the etching, characterized by nitriding the gate insulating film, after having formed the gate insulating film, to improve electron mobility on a first interface, a second interface, and a third interface in the vicinity of the drive point, wherein said first interface is defined between the gate insulating film and the semiconductor substrate (1, 2), said second interface is defined between the gate insulating film and the semiconductor region, and said third interface is defined between the semiconductor substrate (1, 2) and the semiconductor region, and wherein the first interface, the second interface, and the third interface in combination define said drive point, wherein the nitriding is a high temperature annealing in an atmosphere containing at least one selected from the group consisting of N2O, NO and NOx. a semiconductor substrate (1, 2) made of at least one selected from the group consisting of silicon carbide, gallium nitride and diamond, a semiconductor region made of at least one selected from the group consisting of single crystal silicon, polycrystal silicon, amorphous silicon, germanium and gallium arsenide, said semiconductor region being configured to contact a first main face of the semiconductor substrate (1, 2) and different from the semiconductor substrate (1, 2) in band gap, the gate electrode contacting, via a gate insulating film made of silicon dioxide, a part of a junction part between the semiconductor region and the semiconductor substrate (1, 2), the source electrode configured to connect with the semiconductor region, and the drain electrode configured to make an ohmic connection with the semiconductor substrate (1, 2), the method comprising the following sequential operations: forming the semiconductor region on the first main face of the semiconductor substrate (1, 2); etching a part of the semiconductor region; and forming the gate insulating film both on the semiconductor region that is etched and the semiconductor substrate (1, 2) that is exposed after the etching, forming the semiconductor region on the first main face of the semiconductor substrate (1, 2); etching a part of the semiconductor region; and forming the gate insulating film both on the semiconductor region that is etched and the semiconductor substrate (1, 2) that is exposed after the etching, characterized by nitriding the gate insulating film, after having formed the gate insulating film, to improve electron mobility on a first interface, a second interface, and a third interface in the vicinity of the drive point, wherein said first interface is defined between the gate insulating film and the semiconductor substrate (1, 2), said second interface is defined between the gate insulating film and the semiconductor region, and said third interface is defined between the semiconductor substrate (1, 2) and the semiconductor region, and wherein the first interface, the second interface, and the third interface in combination define said drive point, wherein the nitriding is a high temperature annealing in an atmosphere containing at least one selected from the group consisting of N2O, NO and NOx.