A method for manufacturing a semiconductor device includes forming a buffer layer made of a nitride semiconductor, forming a channel layer made of a nitride semiconductor over the buffer layer, forming a barrier layer made of a nitride semiconductor over the channel layer, forming a cap layer made of a nitride semiconductor over the barrier layer, forming a gate insulating film so as to in contact with the cap layer; and forming a gate electrode over the gate insulating film, wherein compression strains are generated at an interface between the cap layer and the barrier layer and an interface between the channel layer and the buffer layer and a tensile strain is generated at an interface between the barrier layer and the channel layer by controlling compositions of the cap layer, the barrier layer, the channel layer, and the buffer layer.