Current–voltage characteristics of an inverted GaAs–AlGaAs modulation doped transistor are calculated using a charge control model. Our calculations show that the electron concentration of the two dimensional electron gas for the inverted structure is comparable to those obtained in normal MODFET’s. The optimum design of an inverted device calls for a doped AlGaAs layer thin enough to be fully depleted. The sheet carrier concentration of the two dimensional electron gas will be only slightly less than the maximum possible. For such devices the predicted transconductances are close to those for normal modulation doped transistors.