A method of forming a semiconductor device having a quantum well structure, comprises the steps of: (a) forming a well film at a first temperature, the well film being made of a III-V nitride semiconductor containing nitrogen, indium and gallium; (b) forming a first barrier film on the well film, the first barrier film being made of a III-V nitride semiconductor containing nitrogen, indium and gallium, and an indium composition of the first barrier film being smaller than that of the well film; (c) changing temperature without forming a semiconductor film; and (d) forming a second barrier film at a second temperature higher than the first temperature, the second barrier film being made of a III-V nitride semiconductor on the first barrier film, the first barrier film being formed at a third temperature, the third temperature being equal to or higher than the first temperature, and the third temperature being lower than the second temperature.