Heat treatments were carried out on native oxide films grown on Hg1-xCdxTe by a photochemical process. The thermal stability of such layers was assessed by monitoring changes in depth profiles obtained from x-ray photoelectron spectroscopy in conjunction with argon ion sputtering. After annealing, photochemical oxides grown in N2O showed a large change in the oxide/Hg1-xCdxTe interface width and a movement of the Cd and Te interfaces towards the oxide surface. These results are comparable to previous studies carried out on anodically grown oxides by other workers. For photochemical oxides grown in an O-2 ambient at slightly higher temperatures, the oxide/Hg1-xCdxTe interface was observed to be very stable under the same annealing conditions, with no observable change in the oxide/Hg1-xCdxTe interface width and no movement of the individual element interfaces. For both the N2O and O-2 grown oxides, there was a significant loss of Hg from the oxide for extended annealing at 250 degrees C in a vacuum of 10(-5) Torr.