We report on the effect of vacuum anneal on interfacial oxides formed between Al 2 O 3 and III–V semiconductors. On InGaAs, no interfacial oxide is detected after annealing at 600 °C under UHV whereas annealing under secondary vacuum favours the regrowth of thin InGaO x interfacial oxide. Lowering the temperature at 400 °C highlights the effect of III–V substrates since In–OH bonds are only formed on InAs by OH release from TMA/H 2 O deposited alumina. On InGaAs, regrowth of InGaO x is observed, as a result of preferential oxidation of Ga. On InP, a transition from InPO x to PO x is highlighted.