In this paper, an approach to determine the average In composition in InGaN/GaN multiple quantum wells (MQWs) was suggested. The period thickness and the average lattice constants (< a(epi) > and < c(epi) >) of MQWs were calculated from high-resolution X-ray diffraction (HRXRD). Then by applying the Vegard's law, the average In composition < x > was simultaneously determined by considering the relationship between the lattice constants under strain. At the same time, by using the period thickness, the average In composition was obtained from the simulation of the Rutherford backscattering spectroscopy (RBS). The results obtained from the two techniques are agreeable. So the approach of combining both HRXRD and RBS can tell reliable chemical composition in InGaN/GaN MQWs. (C) 2003 Elsevier B.V. All rights reserved.