The interfaces of InP/InPAs(1 monolayer)/InP samples grown by organometallic vapor-phase epitaxy were investigated by the x-ray crystal truncation rod scattering measurement. The distribution of As atoms around the InPAs heterolayer was clearly revealed in the atomic scale from the measurement. It was shown that the distribution of As atoms into the layer under the InPAs layer was very small and that distribution of As atoms in the InP cap layer was, on the other hand, noticeable and the amount of As atoms was almost the same as that contained in the InPAs heterolayer. These results suggest that the extension of As atoms in the InP layer occurs due to the absorbed As atoms on the InPAs surface or As atoms remaining in the gas phase. Thus, to realize the abrupt InP/InPAs interface, the source-gas change sequence should be controlled to be very abrupt. ©1997 American Institute of Physics.