It is known that by capping InAs/GaAs quantum dots (QDs), photoluminescence (PL) exhibits blue shift because InAs QD shrinks by intermixing of InAs with GaAs matrix. Moreover, stacked structure of InAs QDs on GaAs, which was preferable for QD lasers and vertical cavity surface emitting lasers (VCSELs), shows increased full-width at half-maximum (FWHM) of PL spectrum because QDs expand due to increase in this intermixing effect with the increase in number of stacking of QD/GaAs layers. Here, suppression of this intermixing was successfully tried by inserting an ultra-thin AlAs at the interfaces between InAs and GaAs layers. As experimental results, PL emission exhibited red shift. Furthermore, the size expansion of stacked QD was suppressed, which was confirmed by UHV-AFM. (c) 2007 Published by Elsevier B.V.