Various aspects of tunable barrier transistors that can be used in high power electronics are provided. In one example, among others, a tunable barrier transistor includes an inorganic semiconducting layer; a source electrode including a nano-carbon film disposed on the inorganic semiconducting layer; a gate dielectric layer disposed on the nano-carbon film; and a gate electrode disposed on the gate dielectric layer over at least a portion of the nano-carbon film. The nano-carbon film can form a source-channel interface with the inorganic semiconducting layer. A gate field produced by the gate electrode can modulate a barrier height at the source-channel interface. The gate field may also modulate a barrier width at the source-channel interface.