During the oxidation of the ordered intermetallic compound Co0.6Ga0.4 the main product observed is monoclinic gallium oxide Ga2O3. Due to the loss of gallium, the intermetallic phase decomposes after an induction time to form the cobalt-rich alloy Co0.835Ga0.165. The morphology of the interface between metal and oxide is strongly structured for the metal side. whilst the oxide side of the interface is smooth. The oxidation rate as well as the development of the interface morphology are dependent on the crystallographic orientation of the grains. The observed morphology can be explained by condensation of supersaturated defects in Co0.6Ga0.4 which am chemically induced by selective oxidation of gallium.