A Field Effect Transistor structure is provided having: a semi-insulating substrate; a semiconductor mesa structure disposed on the substrate and having a notch in an outer sidewall of the mesa structure; a source electrode disposed within the opposing sidewalls in ohmic contact with a source region of the mesa structure; a drain electrode disposed within the opposing sidewalls in ohmic contact with a drain region of the mesa; and a gate electrode, having an inner portion disposed between, and laterally of, the source electrode and the drain electrode and in Schottky contact with the mesa structure, extending longitudinally towards the notch and having outer portions extending beyond the mesa structure and over portions of the substrate outside of the mesa structure. In one embodiment, the mesa structure includes a pair of notches projecting inwardly towards each other and the inner portion of the gate extends longitudinally between the pair of notches.