We report a blue-shifted photoluminescence (PL) of closely stacked InAs/GaAs quantum dots (QDs) grown via molecular beam epitaxy on GaAs(1 0 0) substrates. Room temperature PL and chemical etching were used to isolate and characterize the quantum dot layers. PL measurements showed that there is a significant shifting to higher energy caused by the deposition of a second layer of QDs. Such shifting is present only in closely stacked QD layers. This would imply that the first QD layer capped with a 100 Angstrom GaAs generates a strain field that not only causes vertical alignment but could also lead to the formation of a second QD layer with different structure and dimension than the first QD layer grown. (C) 2002 Elsevier Science B.V. All rights reserved.