This paper compares the results obtained from wet oxidation in vapor mixture of methanol-water with those from wet oxydation water vapor of AlAsxSb1-x layers in arsenic based structures matched on InP and On InAs subtrates. All the structures have been made by molecular beam epitaxy. The quality of the resulting oxide layers (AlOx) were examined by means of scanning electron microscopy (SEM), secondary ions mass spectrometry (SIMS) and resistance measurements of the structures. The results described in this report demonstrate that the addition of methanol into water vapor reduces the amount of antimony and arsenic in the oxidized layers of n-type structures.