A semiconductor device includes: a compound semiconductor layer having a first compound semiconductor layer and a second compound semiconductor layer having a higher melting point than the first compound semiconductor layer; and an insulation gate on the second compound semiconductor layer. The compound semiconductor layer further includes: a drift region; a source region; and a body region between the drift region and the source region. The insulation gate faces the body region. The body region bridges over both the first compound semiconductor layer and the second compound semiconductor layer.