The morphological modifications of plastically relaxed InAs/GaAs quantum dots (QDs) are studied by transmission electron microscopy (TEM) and interpreted on the basis of energy calculations. The growth of a GaAs cap-layer over the dislocated QDs leads to a significant increase of their size, and to a decrease of their In-composition, due to In/Ga exchange and interdiffusion reactions. A mechanism of de-relaxation of the QDs leading to the disappearance of the dislocation network at the bottom InAs/GaAs interface is observed as a consequence of these structural modifications. Our calculations show that this de-relaxation process is energetically favorable below a critical In-composition of the QDs, which is reached during the growth of the GaAs cap-layer due to In/Ga interdiffusion. (C) 2007 Elsevier B.V. All rights reserved.