a substrate including a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type at a surface;

first and second gate insulating films disposed on the first and second semiconductor layers, respectively;

a first gate electrode disposed on the first gate insulating film, and including a first conductive layer consisting of a nitride of a predetermined metal in contact with the first gate insulating film, the first conductive layer having a first nitrogen concentration; and

a second gate electrode disposed on the second gate insulating film, and including a second conductive layer consisting of a nitride of the predetermined metal in contact with the second gate insulating film, the second conductive layer having a second nitrogen concentration lower than the first nitrogen concentration,

wherein the first conductive layer is formed from a first film consisting of a nitride of the predetermined metal, and the second conductive layer is formed by stacking the first film and a second film consisting of the predetermined metal, and diffusing nitrogen from the first film to the second film by diffusion, and

wherein the first gate electrode further comprises a portion derived from the second film and stacked on the first conductive layer through an electrically-conductive barrier layer for preventing nitrogen diffusion.