Wet oxidation of AlGaAs to formAl2O3by the reduction ofH+from water to H produces intermediateAs2O3.Reduction ofAs2O3by H to elemental As enables the escape of arsenic from the oxidized film. Further reduction of As toAsH3can provide another volatile As species. Formation of intermediate As is problematic for the use of wet oxidation in metal-insulator-semiconductor applications. The kinetic balance betweenAs2O3formation and As escape can explain the transition between the linear and parabolic time dependence of the wet oxidation of buried AlGaAs layers. The near-total suppression of wet oxidation byO2is attributed to the suppression of volatile product formation through consumption of atomic hydrogen by reaction withO2to formH2Oin preference to the hydrogen reduction ofAs2O3.©1997 American Institute of Physics.