The electronic structures at the interface of aluminum tris(8-hydroxyquinoline) (Alq(3))/Al2O3/Al have been determined by ultraviolet photoemission spectroscopy measurements and compared to similar measurements of the Alq(3)/Al interface. In the Alq(3)/Al2O3/Al study, shift of the highest occupied molecular orbital level of the Alq(3) layer was observed when compared to that of Alq(3)/Al. An energy level alignment diagram was proposed, showing that the lowering of the driving voltage achieved in organic electro-luminescent devices with a thin Al2O3 layer between the aluminum cathode and the Alq(3) him can be attributed to the reduction of the barrier height for electron injection. The electronic structures of Alq(3) grown on Ga and its oxide have also been studied.