Abstract: This disclosure relates to two-terminal solid state microwave devices, such as transferred electron and avalanche effect devices, comprising a high-conductivity semiconductor substrate formed over at least a part of one major surface with an active layer of semiconductor material, a first contact providing electrical contact with the active layer to define the active region of the device, and a second contact on the same side of the substrate, providing a relatively low impedance contact to the substrate in operation of the device at the operating bias current for the active region.To simplify fabrication, both contacts may have substantially identical structures with the second contact also overlying the active layer.