A field effect transistor includes a vertical fin-shaped semiconductor active region having an upper surface and a pair of opposing sidewalls on a substrate, and an insulated gate electrode on the upper surface and opposing sidewalls of the fin-shaped active region. The insulated gate electrode includes a capping gate insulation layer having a thickness sufficient to preclude formation of an inversion-layer channel along the upper surface of the fin-shaped active region when the transistor is disposed in a forward on-state mode of operation. Related fabrication methods are also discussed.