Microwave integration has so far been pursued with Schottky gate f.e.t.s where difficulties however exist with : (1) the Schottky contact which must not be biased strongly in forward direction without danger of damaging it, (2) the high d.c. standby power dissipated as compared with normally-off digital transistors with reasonably large signal levels which are unfortunately not possible with m.e.s.f.e.t.s, and (3) with the rather small d.c. input impedance. The use of a GaAs m.o.s.f.e.t. technology avoids these and other difficulties and allows more flexibility in the circuit design.Until recently it was not possible to produce satisfactory m.o.s. structures on GaAs with sufficiently low leakage currents and satisfactory interface properties. Satisfactory results have now been achieved with an anodic oxidation process which has resulted in various transistors operating in each of the three modes of enhancement, inversion and depletion. Technological details of the manufacture of these devices are described and experimental results presented which demonstrate some of their useful ranges of operation. Possibilities of integration are reviewed and finally the areas of immediate applications for such integrated circuits discussed.