A compound field effect transistor having multiple pinch-off voltages comprising: first and second field effect transistors, each field effect transistor comprising a semiconductor layer, the semiconductor layer having an electrically conducting layer therein; an ohmic contact layer on the semiconductor layer; a source and a drain on the ohmic contact layer; at least one gate on the semiconductor layer between source and drain; at least one gate of the first transistor and one gate of the second transistor being matched gates, each gate having the same effective thickness of electrically conducting layer beneath it but the gates having different gate lengths.