A quadrupole mass spectrometer was used to measure the desorption rate of oxides produced by adsorption of oxygen on GaAs polar {111} crystal planes. The results suggest that oxygen is adsorbed dissociatively at Ga surface atoms and is desorbed as Ga2O in a first‐order process with an activation energy of 54±4 kcal/mole from the (111) face and 42±4 kcal/mole from the (1¯1¯1¯) face. In agreement with previous work, O2sticking probability was∼10−4at low coverage; however, no activation energy for adsorption was detected for the (111) face. Desorption of Ga2O from the (1¯1¯1¯) surface showed evidence of an additional, weaker binding state not present on the (111) surface.