Nanoindentation tests were conducted on single-crystal indium phosphide (InP) using a Vickers indenter and a spherical indenter over a wide load range. The resulting indents were examined using scanning electron microscopy, cross-sectional transmission electron microscopy and selected area diffraction. Effects of the indenter type and indentation load on the surface cracking behavior, load–displacement characteristics and subsurface damage were investigated. The results showed that the cracking behavior and critical load for crack generation depends strongly on the indenter geometry and orientation. Pop-in events occur during loading in the case of the spherical indenter, but not in the case of the Vickers indenter. It was demonstrated that dislocations dominate the deformation mechanism, and no phase transformation occurs. The indenter contact immediately causes a high-density dislocation region, below which extend slip bands. The stress field of the indented zone was simulated by the finite element method, and the stress concentration regions corresponded to the high-density dislocation regions.