The field effect transistor (FET) of the present subject matter comprises a bottom gate electrode, a bottom gate dielectric provided on the bottom gate electrode, a channel layer provided on the bottom gate dielectric. A top portion comprising a source electrode, a drain electrode, a top gate electrode provided, and a top dielectric layer is provided on the channel layer. The channel layer forms Schottky barriers at points of contact with the source and the drain electrode. A back-gate voltage varies a height and a top-gate voltage varies a width of the Schottky barrier. The FET can be programmed to work in two operating modes-tunnelling (providing low power consumption) and thermionic mode (providing high performance). The FET can also be programmed to combine the tunnelling and thermionic mode in a single operating cycle, yielding high performance with low power consumption.