The split-gate concept has been applied to dual-gate high electron mobility structures for room-temperature operation. The gates are configured so that the second gate is in close proximity to the gap defined by the split-gate electrodes. This allows both gates to control the carrier density in the same region of the device, so that it is possible to control the threshold voltage for either gate by altering the bias at which the other gate is held. The effect of changing the gate configuration is demonstrated. ©1997 American Institute of Physics.