The effect of scratch proximity on the resistance to plastic deformation in InP (100) crystals under low normal loads has been studied using atomic force microscopy (AFM) and transmission electron microscopy. Plastic flow has been observed for scratches performed with an atomic force microscope along {110} and {100} crystallographic directions. Plastic hardening has been determined from AFM measurements of the scratch depth and width, as a function of the distance between parallel scratches. For relatively low loads, hardening is found to be independent of the crystallographic direction of the scratch. Significant hardening takes place for scratch separations of less than ∼80 nm. Analysis of the microstructure indicates that hardening occurs due to the interaction of dislocations generated at adjacent scratches and acting on different slip planes. © 2011 American Institute of Physics.