Abstract: A high-electron mobility transistor or HEMT has a top surface layer between its gate and drain arranged to produce a channel to drain conductance that is close to the ungated channel conductance to lower the output conductance and reduce gate leakage and gate capacitance. The transistor has a high band-gap active layer to produce a 2DEG channel in an adjacent layer, and source, gate and drain electrodes on the active layer. An undoped or lightly doped surface layer in the region between the gate and the drain produces a low conductance for a region of a few hundred .ANG. from the drain-side edge of the gate. This spreads the electric field domain over at least this few hundred .ANG. distance.