Native oxide has been found to have a noticeable effect on the mechanical deformation of InP during nanoindentation. The indentations were performed using spherical diamond tips and the residual impressions were studied by atomic force microscopy. It has been observed that in the early stages of mechanical deformation, plastic flow occurs in the oxide layer while the indium phosphide is still in the elastic regime. The deformed native oxide layer results in a pile-up formation that causes an increase in the contact area between the tip and the surface during the nanoindentation process. This increase in the projected contact area is shown to contribute to the apparent high pressure sustained by the crystal before the onset of plastic deformation. It is also shown that the stress necessary to generate the first dislocations from the crystal surface is ∼3 GPa higher than the stress needed for slip to occur when dislocations are already present in the crystalline structure. © 2008 American Institute of Physics.