Thermal instability of anodic sulfide films on Hg1−xCdxTe was studied. Instead of using laser ionization or ion backscattering in studying oxidic films after heat treatment, we used x‐ray photoelectron spectroscopy (XPS) in analyzing nonaqueous sulfidization. In this case, XPS is feasible, simpler, and has the advantage of better resolution. Hg evaporation was investigated here by measuring Te(3d5/2) of Te oxide peak rather than Hg lines. Correlation between thermal instability and compositionxwas obtained.