We investigated the segregation of Sb on InP in metalorganic vapour phase epitaxy (MOVPE). A clean PH3 stabilized InP(001) surface is exposed to trimethyl antimony (TMSb) and then immediately overgrown with InP. For a single exposure and overgrowth cycle a self-organized InPSb double-quantum well (QW) is formed, one layer is at the Sb-treated surface and the other occurs after 50-150 nm overgrowth. This behaviour was found in situ by RAS and verified ex situ by SIMS and XRD. The separation of the second QW linearly depends on the growth temperature in a range from 520 to 580 degrees C. At temperatures above 580 degrees C the separation saturates due to desorption. We propose strain-induced surface melting to explain the double quantum well QW formation. (c) 2006 Published by Elsevier B.V.