PURPOSE: To obtain a field-effect transistor operated at high frequency and high speed by forming an AlGaAs layer between an InGaAs operating layer and a gate electrode as a gate insulating layer.

CONSTITUTION: An non-doped Al0.48In0.52As layer 2 is grown on a semi-insulating InP substrate 1, an Al0.48In0.52As layer 3 to which Si is doped is grown further, and a non-doped Al0.48In0.52As layer 4 is grown further as a spacer. A lattice- matched non-doped In0.53Ga0.47As layer 6 is grown on the layer 4, and a two-dimensional electron gas layer 5 is shaped. A non-doped Al0.3Ga0.7As layer 7 is grown further on the layer 6, and a gate electrode 9, a source electrode 8 and a drain electrode 10 are formed. Accordingly, high breakdown strength is acquired in both forward and reverse bias directions, thus reducing leakage currents.