We investigate both theoretically and experimentally the effects of the In surface segregation in InGaN/GaN quantum wells (QWs). It is shown that this phenomenon induces a blue-shift of the QW photoluminescence (PL) energy, which does not depend on the QW width, at least for well thicknesses larger than 1.5 nm. The oscillator strength of the QW optical transitions decreases when the segregation process increases due to the spatial separation of the electron and hole pairs by the internal electric field. The surface segregation phenomenon has been studied by reflection high-energy electron diffraction in the case of molecular beam epitaxy growth with NH3 as the nitrogen source. Evidence for surface segregation is given by comparing PL results and data deduced from a careful analysis of the growth rate variation of GaN deposited on an In covered surface. (C) 2003 Elsevier Science B.V. All rights reserved.