We have used x-ray photoelectron spectroscopy to investigate electron cyclotron resonance oxygen plasma oxidation and hydrogen plasma deoxidation of GaAs surfaces. Experimental evidence shows that ECR oxidation at room temperature forms a stoichiometric oxide layer that is primarily composed of As2Os and Ga2O3. A hydrogen plasma is shown to clean GaAs surfaces and recover surface order, even at room temperature. Sample heating (200–300 °C) expedites the removal of Ga2O3 and improves surface order. In addition, no significant differences in oxidation and deoxidation were observed for sample biasing, either positively or negatively. © 1991, American Vacuum Society. All rights reserved.