Transistors with metal oxide channel material and a multi-composition gate dielectric. A surface of a metal oxide gate dielectric may be nitrided before deposition of a metal oxide channel material, for example to reduce gate capacitance of a TFT. Breakdown voltage and/or drive current of a TFT can be increased through the introduction of an additional metal oxide and/or nitride between the gate electrode and a metal oxide gate dielectric. The introduction of an intervening layer between two layers of a metal oxide gate dielectric can also increase breakdown voltage and/or drive current of a TFT.