The surface segregation of indium (In) atoms was investigated during the growth of InGaAs layers by reflection high-energy electron diffraction (RHEED). We showed that the strong damping of the RHEED oscillations usually observed during the deposition of InGaAs on GaAs was directly related to the presence of a population of In atoms at the surface of the sample originating from the segregation phenomenon in the InGaAs layers. We proposed a simple model to estimate the segregation coefficient R in situ and in real time from the RHEED oscillations. Our results were quantitatively confirmed by several RHEED measurements carried out under very different growth conditions and were in excellent agreement with data from the literature. (C) 2002 Elsevier Science B.V. All rights reserved.