It is shown that standard electron spectroscopy techniques such as Auger electron spectroscopy (AES) and electron loss spectroscopy (ELS), when associated with MBE systems, may provide useful information about the clean surface composition changes induced by vacuum annealing of III–V binary or multinary semiconductors. As an illustration of the potential of these types of techniques, annealing experiments were carried out on InP, and on AlxGa1−xAs,AlxIn1−xAs, and GaxIn1−xAs ternary alloy semiconductors grown in situ by MBE. In the case of InP annealing, AES measurements show that phosphorus has a complex behavior near the surface involving several competitive mechanisms. A critical temperature Tc≂450 °C is observed for these mechanisms, leading to an increase of the phosphorus surface concentration for temperature of annealing Ta<Tc and to a sharp decrease for Ta>Tc. In addition to this result, a study by ELS clearly indicates that indium clustering occurs in the 450–500 °C temperature range. The arsenide alloys exhibit a systematic shift of the surface composition under annealing. For AlxGa1−xAs, above Tc≂550 °C the surface composition evolves towards AlAs with increasing Ta. An even more drastic modification of surface composition is found for AlxIn1−xAs and GaxIn1−xAs: a decrease of In surface concentration is already observed for 450 °C≲Ta≲500 °C. These results are in qualitative agreement with previously reported composition variations of ternary alloy epitaxial layers versus growth temperature determined by Rutherford backscattering and depth profiling Auger analyses.