A semiconductor device includes a lower barrier layer 12 composed of a layer of AlxGa1-xN (0≦x≦1) in a state of strain relaxation, and a channel layer 13, which is composed of a layer of InyGa1-yN (0≦y≦1) disposed on the lower barrier layer 12, has band gap that is smaller than band gap of the lower barrier layer 12, and exhibits compressive strain. A gate electrode 1G is formed over the channel layer 13 via an insulating film 15 and a source electrode 1S and a drain electrode 1D serving as ohmic electrodes are formed over the channel layer 13. The insulating film 15 is constituted of polycrystalline or amorphous member.