Field effect transistor of the MESFET type for high frequency applications and method of manufacturing such a transistor

A field effect transistor for high-frequency applications comprising a semi-insulating monocrystalline substrate, a thin active n-doped layer of a material having a high electron mobility on said substrate, a metallic layer comprising two metallic layer portions comprising two ohmic contacts which form the source and drain contact regions of the transistor on the surface of said active layer, between which a metallic contact is provided on said active layer to form a gate electrode of the Schottky type, characterized in that a dielectric layer is disposed on and in direct contact with the active layer, said direct contact being over the entire extent of said dielectric layer between the source contact region and gate electrode and between the gate electrode and drain contact region, and in that the metallic layer comprising the ohmic contacts has a further part which extends continuously on the dielectric layer and forms a capacitance with said dielectric layer and only portions of said active layer other than said source and drain contact regions without contacting the gate electrode.