A semiconductor device includes: a substrate comprised of gallium nitride; an active layer provided on the substrate; a first buffer layer that is provided between the substrate and the active layer and is comprised of indium aluminum nitride (InxAl1−xN, 0.15≦x≦0.2); and a spacer layer that is provided between the first buffer layer and the active layer and is comprised of aluminum nitride having a thickness of 1 nm or more to 10 nm or less.