GaAs surfaces cleaved in ultrahigh vacuum and cooled to 100 K [low temperature (LT)] were exposed to molecular oxygen. Band bending as a function of exposure was measured with ultraviolet photoemission spectroscopy. Band bending on LTp‐GaAs is very small up to exposures>106L, whereas the same exposures give considerable band bending at room temperature (RT). Band bending on LTn‐GaAs is as fast as at RT. This situation is therefore opposite to that of metals/LT GaAs reported last year at this conference, but is analogous to that produced by Cl/GaAs at RT. These results can be interpreted in terms of simple adsorption of electronegative species which introduce an acceptor level deep in the GaAs gap. As for metals on LT GaAs, the nature of the surface states induced by the adsorption of single species dominates the position ofEFat low coverage. Metallicity dominates at high coverages of metals; oxidation‐induced defects dominate at RT or at higher exposures for O2/GaAs.