HEMT with a graded InGaAlP layer separating ohmic and Schottky contacts

A semiconductor device comprises: a GaAs substrate; a buffer layer provided on the GaAs substrate; a laminated structure provided on the buffer layer; a Schottky contact layer provided on the laminated structure; a n-type In_x(Ga_1-;yAl_y)_1-;xP layer provided on the Schottky contact layer; a n-type In_u2Ga_1-;u2As ohmic contact layer provided on the n-type In_x(Ga_1-;yAl_y)_1-;P layer; a gate electrode provided on the Schottky contact layer; and a source electrode and a drain electrode provided on the ohmic contact layer. The buffer layer is made of a semiconductor, and at least a part of the semiconductor has a lattice constant larger than a lattice constant of GaAs. The channel layer is made of In_u1Ga_1-;u1As, and the electron supply layer is made of n-type In_v1Al_1-;v1As. At least a part of the Schottky contact layer is made of non-doped In_v2Al_1-;v2As. The In_x(Ga_1-;yAl_y)_1-;xP layer has a part where a bandgap has a distribution which shows a gradual or a stepwise decrease from the Schottky contact layer toward the ohmic contact layer.