PURPOSE: To increase mutual conductance and reverse dielectric resistance by forming a layer, resistivity thereof is higher than a channel region and thickness thereof is brought to a depletion state by the diffusion potential of a gate metal, between the channel region and a gate electrode.

CONSTITUTION: A source region 12 and a drain region 13 are formed to a semi- insulating GaAs substrate 11. Si3N4 is deposited on the surface as an insulating film 19, and a window hole section is formed to the film 19 in a gate region section, the exposed section of a channel region is etched, and a high resistivity layer 20 is grown on the etched section. With the layer 20, the thickness is all brought to a depletion state by the diffusion potential of a gate metal, and it has resistivity higher than the channel region. Al is evaporated, and the gate metal 15 is formed through a lift-off method. Accordingly, a Schottky gate type FET having large mutual conductance and large gate reverse dielectric resistance can be manufactured.