A storage transistor has a tunnel dielectric layer and a charge-trapping layer between a channel region and a gate electrode, wherein the charge-tapping layer has a conduction band offset that is less than the lowering of the tunneling barrier in the tunnel dielectric layer when a programming voltage is applied, such that electrons direct tunnel into the charge-trapping layer. The conduction band of the charge-trapping layer is has a value between −1.0 eV and 2.3 eV. The storage transistor may further include a barrier layer between the tunnel dielectric layer and the charge-trapping layer, the barrier layer having a conduction band offset less than the conduction band offset of the charge-trapping layer.