The evolution of interface formation between MgO and the atomically clean In0.53Ga0.47As is studied by synchrotron radiation based photoemission. The deposition of MgO in a step wise fashion on the decapped In0.53Ga0.47As surface at room temperature results in the growth of an ultrathin interfacial oxide layer. Subsequent thermal annealing at 400 °C led to the reduction of the As and In oxides and the appearance of a Ga oxide component. The deposition of metallic Mg resulted in the further removal of the interfacial oxide and the out diffusion of In into the overlayer indicating severe disruption of the interface. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.