Abstract: A compound semiconductor device including a field effect transistor particularly suited for high frequency applications such as grounded source applications. An active layer is formed on one surface of a compound semiconductor substrate. An aperture is dry etched through the second surface of the semiconductor substrate toward the first surface, and terminates in the source region of the active layer. The walls of the aperture are metallized as is the second surface of the substrate. A gate electrode and at least a drain electrode are formed on the first surface. The metallized second surface can act as a source electrode by virtue of ohmic contact between the metallized walls of the aperture and the source region of the active layer.