A new equivalent circuit is given for the GaAs m.e.s.f.e.t., which includes resistive loss in the feed back elements. The circuit values are given for several 1 μm-gate GaAs m.e.s.f.e.t.s. A method for fitting s12 to the measured data is described. Finally, the gain and stability factor of several GaAs m.e.s.f.e.t.s. are extrapolated to 24 GHz from the present model.