A method of producing a MESFET which includes forming a refractory metal gate structure on an active layer formed in or on a semiconductor substrate. Source and drain regions optionally with extensions, are formed adjacent the gate structure. An insulating film is deposited over the partly formed structure to form a film portion on the semiconductor substrate which is separated from further film portions formed over the source and drain regions. A flattening resist is deposited over the insulating film and etched to expose only the film portion on the gate structure, while the gate structure itself and the resist protects the film portions on the source and drain regions. The film portion over the gate structure can thus be removed without damage to the gate structure or the remainder of the insulating film. The process produces with increased yield and more consistent properties in that the danger of attacking the refractory metal gate structure during operations succeeding its formation is significantly reduced.