Using a simple but novel method of analysis, the voltage drop across the oxide (pad-oxide) in the oxide:nitride dual dielectric is determined for both positive and negative gate polarities. From the Fowler-Nordheim plot of the oxide voltage drop, the electron barrier from nitride to oxide is 3.2 ± 0.2 eV. However, the current injection from the nitride electrode is about 7 orders of magnitude lower than the current injection from the silicon electrode under the same oxide field values. This large field-current difference between the two directions of electron injection is consistent with the large difference observed in the J ★ t (charge fluence to breakdown) data.