An MESFET is configured wherein a semiconductor layer structure including an i-AlGaAs buffer layer, an n-AlGaAs electron supply layer having an impurity doping density ranging from 110¹⁷ cm^-3 to 110¹⁸ cm^-3 and a layer thickness ranging from 1 nm to 10 nm, and an n-GaAs channel layer, all of which are sequentially deposited from the semi-insulating GaAs substrate side, is disposed on the semi-insulating GaAs substrate, a gate electrode is provided on the n-GaAs channel layer, and a source electrode and a drain electrode opposite to each other with the gate electrode interposed therebetween are provided.