In this work we present an in situ investigation of the interface composition between an In sub (0. 53) Ga sub (0. 47) As substrate and an Al sub (2) O sub (3) oxide grown by molecular beam deposition in ultra high vacuum conditions. In the effort to improve the chemical quality of the interface, reduction of semiconductor-oxygen bonding at the interface can be obtained by growing a few Aa thick pure Al layer before starting exposure of the surface to the atomic oxygen flux. Conversely, when a Ge interface passivation layer is intercalated between the semiconductor and the oxide stack, the interface chemistry is governed by Ge reaction with other species(Al, O), leading only to a partial suppression of the interface oxides.