A normally OFF field effect transistor (FET) having a plurality of contiguous nitride semiconductor layers having different composition and heterojunction interfaces, wherein when there is no potential difference between a first gate and a common ground voltage, a two dimensional electron gas (2DEG) is present at a plurality of heterojunctions in each of a source access region and a drain access region, and substantially no 2DEG is present adjacent any regions of the heterojunctions under the first gate.