The electron-stimulated oxidation of perfect and facetted GaAs(111) 2×2-Ga surfaces has been studied up to 3 nm, by quantitative Auger analysis. After a top oxygen layer has been adsorbed, oxidation progresses by a layer-by-layer mechanism with separate Ga and As oxide phases. On perfect surfaces, one-third of each As monolayer remains embedded in the Ga2O3 formed, indicating that the oxidation proceeds by an ordered breaking of the As bonded to Ga. However, on facetted surfaces all of the oxidized As atoms are desorbed from the surface and only Ga2O3 is detected. Therefore, the formation of As oxides depends on the surface structure, but never these As oxides are buried at the Ga2O3/GaAs interface as it was suggested before.