A method of manufacturing a transistor device includes forming a compound semiconductor material on a semiconductor carrier, forming a source region and a drain region spaced apart from each other in the compound semiconductor material with a channel region interposed between the source and drain regions, forming a Schottky diode integrated with the semiconductor carrier, and forming contacts extending from the source and drain regions through the compound semiconductor material and in electrical contact with the Schottky diode so that the Schottky diode is connected in parallel between the source and drain regions.