PURPOSE: The enhance the reverse directional withstand voltage between the gate and drain by a method wherein the doping of two operating layers is performed independently.

CONSTITUTION: On a semiconductor substrate 11, a shallow operating layer 16 is provided under a Schottky gate electrode 13, a deep operating layer 17 under the source electrode 14 and the clearance between the electrodes 13 and 14, and a deep operating electrode 18 under the dran electrode 15 and the clearance between the electrodes 13 and 15. Where, the resistance between the gate and source can be reduced sufficiently by performing doping by desired amount into the region of the operating layer 17 under the electrodes 13 and 14. Since the doping amount of the region of the operating layer 18 is determined independently of that of the region of the operating layer 17, the reduction of the resistance between the gate and drain is performed by doping within a limit wherein the reverse directional withstand voltage between the gate and drain is not damaged. Therefore, the reverse directional withstand voltage between the gate and drain is secured sufficiently, and simultaneously the resistance between the gate and source and that between the gate and drain are reduced, and then gm is enhanced.