The atomic‐level heterointerface structures of InP samples that contain growth interrupted and AsH3‐exposed surface, with 20 A˚ thick cap layer, were revealed by x‐ray crystal truncation rod scattering measurement. The As atom distribution, the thickness of the cap layer, and the tetragonal distortion of the lattices were obtained from the samples that have only single modified layer in the whole InP wafer. The calculated total amounts of As matched well with the value obtained by fluorescence x‐ray analysis. ©1995 American Institute of Physics.