An Impact Ionization Field-Effect Transistor (I-MOS) device in which device degradation caused by hot carrier injection into a gate oxide is prevented. The device includes source, drain, and gate contacts, and a channel between the source and the drain. The channel has a dimension normal to the direction of a charge carrier transport in the channel such that the energy separation of the first two sub-bands equals or exceeds the effective energy band gap of the channel material.