A method for producing a semiconductor device (20) is disclosed. The semiconductor device (20) includes: 1) a semiconductor substrate (1, 2), 2) a hetero semiconductor area (3) configured to contact a first main face (1A) of the semiconductor substrate (1, 2) and different from the semiconductor substrate (1, 2) in band gap, 3) a gate electrode (7) contacting, via a gate insulating film (6), a part of a junction part (13) between the hetero semiconductor area (3) and the semiconductor substrate (1, 2), 4) a source electrode (8) configured to connect to the hetero semiconductor area (3), and 5) a drain electrode (9) configured to make an ohmic connection with the semiconductor substrate (1, 2). The method includes the following sequential operations: i) forming the gate insulating film (6); and ii) nitriding the gate insulating film (6).