This invention has an objective to provide a field effect transistor semiconductor which has great adhesiveness between a gate metal and an insulating film defining a gate electrode end and to improve production yield thereof. The field effect transistor semiconductor of this invention comprises a source/drain electrode 6 positioned in a predetermined position in a GaAs substrate 1, a channel region provided in the GaAs substrate 1 and between the source/drain electrodes 6, a gate electrode 11 which is in schottky contact with a part of a channel region and is positioned between the source/drain electrodes 6, and an insulating film 7 which electrically insulates a surface of the GaAs substrate and the gate electrode 11 at both side surfaces of the gate electrode 11. The gate electrode 11 covers a part of the insulating film 7 and the surface of the GaAs substrate serving as the channel region, and a bottom metallic layer 8 contained in the gate electrode 11 is covered with a second metallic layer 9 which is highly adhesive to the insulating film 7.