A normally-off transistor with a high operating voltage is provided. The transistor can include a barrier above the channel and an additional barrier layer located below the channel. A source electrode and a drain electrode are connected to the channel and a gate electrode is connected to the additional barrier layer located below the channel. The bandgap for each of the barrier layers can be larger than the bandgap for the channel. A polarization charge induced at the interface between the additional barrier layer below the channel and the channel depletes the channel. A voltage can be applied to the bottom barrier to induce free carriers into the channel and turn the channel on.