Photoluminescence (PL) of self-assembled InAs quantum dots (QDs) on GaAs substrate with different ln(Al)GaAs cap layer are studied. It is now well known that the peak position of the InAs QDs covered with InGaAs layer shifts to longer wavelength than those covered with GaAs and AlGaAs. The theoretical simulations are developed to distinguish various contributions to the wavelength shift from the dot height, strain, and barrier height of different cap layers. It reveals that most of the stress in the InAs QDs comes from the upper GaAs cap layer. (c) 2005 American Vacuum Society.