The photoconductivity in the 1–6 eV energy range was measured for Al 2O 3 prepared in three different ways with Mg, Al and Au counterelectrodes. C-V curves were taken on AlAl 2O 3p-Si and AuAl 2O 3p-Si devices. The leakage currents of NaAl 2O 3Al sandwiches were measured. From these measurements the barrier at the metal-oxide conduction band was found to be 3.5 ± 0.2 eV for Al. The photoconductivity with a threshold of about 2 eV is shown not to be due to the emitting metal electrodes for all three metals used. This threshold is independent of the work function of the counterelectrode.