The initial stages of oxidation of AlAs(001)(using D2O as the oxidant) have been investigated using Auger electron spectroscopy and temperature-programmed desorption. We have found that molecularly adsorbed water on AlAs(001) has two competing reaction pathways available : either desorption back into the gas phase, or dissociation resulting in aluminum oxide, aluminum hydroxide, and arsenic hydride. Recombination of the arsenic hydride produces arsine, which desorbs and depletes arsenic within the oxide film, a process which is shown to enhance the oxide growth. By identifying the various reaction steps that occur (with annealing) after the low-temperature adsorption of water on AlAs(001), we are able to propose a mechanism for the initial stages of wet AlAs oxidation.