Composition and stress dependences of InP/Ga(x)Inx(1-x)As(y)P(1-y)/InP interface structures were investigated using X-ray crystal truncation rod (CTR) scattering measurements, in order to realize why group-III atoms were always distributed widely around hetero-interfaces between InP and GaInAs(P). The result showed that the change of the Ga and As compositions to keep the lattice constants and the change of the stress to keep the Ga composition did not affect the degree of the distribution of the group-III atoms. It suggested that the distribution of the group-III atoms was due neither to mixing of In and Ga nor to relaxing local stress at around the interfaces. The distribution was probably related to the growth process at the surface in the organometallic vapor phase epitaxy (OMVPE) system. (C)2003 Elsevier Science B.V. All rights reserved.