PURPOSE: To provide MESFETs which are simple in structure and excellent in terms of the linearity of input/output characteristics with a high saturation output and a high noise factor.
CONSTITUTION: When annealing a drain layer 3, a source layer 4 and a channel layer 5, an SiN film, which contains a great deal of hydrogen, and, which is not so precise is formed on the surface of a GaAs-made board 2 and annealed in the atmosphere of N2. This construction reduces and eliminates the oxygen on the surface of the GaAs board 2 and opens an annealing film 6 only in the part where a drain electrode 13, a source electrode 14 and a gate electrode 15 are formed as well. It is, therefore, possible to reduce the surface level on the board surface and thin a surface depletion layer.