The chemical composition of surface oxides grown on p-type InP(100) after etching in H2SO4/H2O and in H2SO4/H2O2/H2O etchants was investigated using X-ray nide angle diffraction and glancing angle diffraction techniques. Diffraction from only one lattice set in the matrix oxide was detected in etching with H2SO4/H2O solution by wide angle diffraction. Each diffraction line appeared as an interference pattern, possibly caused by beams reflected from thin layers of indium phosphate hydrate having a single-crystal structure, and showing an extremely preferred orientation and coherent with respect to the substrate. Only one set of reflection peaks was observed in wide angle diffraction, and an interference oscillation was observed in each reflected beam. The dissolution rates of InP in H2SO4/H2O and in H2SO4/H2O2/H2O were determined quantitatively by inductively coupled plasma emission spectrometry. The mixed component oxides and single component products were observed on the oxidized InP. The dissolution rates of InP were almost indiscernible under either illumination or dark. The addition of H2O2 in H2SO4/H2O solution does nor play any critical role in the dissolution of InP.