Enhancement mode MOSFET and depletion mode FET on a common group III-V substrate

The present invention relates to providing an enhancement-mode (e-mode) Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) with a complementary depletion-mode (d-mode) FET on a common group III-V substrate. The depletion mode FET may be another MOSFET, a MEtal-Semiconductor FET (MESFET), a High Electron Mobility Transistor (HEMT), or like FET structure. In particular, the e-mode MOSFET includes a gate structure that resides between source and drain structures on a transistor body. The gate structure includes a gate contact that is separated from the transistor body by a gate oxide. The gate oxide is an oxidized material that includes Indium and Phosphorus. The gate oxide is formed beneath the gate contact.