PURPOSE: To widen the operating voltage range by providing on a second semiconductor layer a third semiconductor layer having a lower conduction band end higher than the lower conduction band end of the second semiconductor layer and becoming a gate section forming a barrier, thereby suppressing the gate leakage current.

CONSTITUTION: On a semi-insulating InP substrate 11, an i-AlInAs layer 12 having a thickness of the order of 2000, an i-GaInAs layer 13 becoming a channel forming layer and having a narrow band gap of the order of 1000, a thin i-AlInAs layer 14 having a wide band gap and a thickness of 50, an n-AlInAs 15 having a wide band gap, a thickness of the order of 500 and an impurity concentration of the order of 2×1018cm-3, and a p+-GaAs layer 16 becoming a gate section and having a thickness of the order of 200 and an impurity concentration of the order of 5×1018cm-3 are sequentially formed by an epitaxial growth. Then, with a metallic gate electrode 17 as a mask the p+-GaAs layer 16 is selectively removed by an RIE (reactive ion etching) method, thereby leaving the p+-GaAs layer 16 only under the gate electrode 17. Since the GaAs layer can be selectively etched by an RIE method with the AlInAs layer 15, such a HEMT 20 can easily be fabricated.