Indium oxide/n-GaAs(110) interfaces fabricated by means of reactive evaporation of indium in the presence of oxygen onto ultrahigh vacuum cleaved GaAs(110) have been studied by means of Auger electron spectroscopy and electron energy loss spectroscopy. The results show that the growth of the indium oxide layers at room temperature under a wide range of oxygen pressures followed the Stransky-Krastanov model. In all cases the presence of In clusters at the interface was observed, and at the high-pressure regime (∼ 1 × 10 -4 Torr) some oxidation of the GaAs surface was noted as well. These results can be correlated to our earlier report [J. Appl. Phys. 69, 1494 (1991)] on the performance of diodes produced under high vacuum conditions.