The oxide field dependence of both the interface state generation and electron trapping during electron injection are studied using transistor structures. Two field thresholds are observed for the generation of interface states, at 1.5 and 4 MV/cm, respectively. The threshold at 4 MV/cm is also found for the generation of electron traps. The 1.5 MV/cm threshold is related to the change in energy loss mechanism of the injected electrons. The threshold at 4 MV/cm is suggested to originate from the injection of holes from the anode.