Scanning tunneling microscopy has been used to investigate the overgrowth of GaAs capping layers on InAs islands formed on GaAs(0 0 1) substrates. It is found that initially, GaAs selectively nucleates just around the InAs islands. Beyond a coverage of 1.5 ML, GaAs sticks to steps. Then, the growth of GaAs proceeds in a layer-by-layer fashion. From the evolution of height distributions of the islands as a function of the coverage of GaAs capping layers, it is found that the overgrowth of GaAs brings about a significant change in the height of the InAs islands (dots). The height of the InAs dots is determined by deposition of GaAs capping layers below 2 ML. (C) 2003 Elsevier Science B.V. All rights reserved.