Doubly stacked InAs quantum dots (QDs) /GaAs structures with different thicknesses of a GaAs spacer layer were grown by organometallic vapor phase epitaxy (OMVPE) and optical properties were investigated by photoluminescence (PL) measurements. A PL spectrum showed Gaussian-like shape with a central wavelength of 1144 nm and an FWHM of 102 nm from doubly stacked InAs QDs with the nominal GaAs spacer layer thickness of 87 nm. The central wavelength and the FWHM are almost the same as those from single layer InAs QDs. On the other hand, an asymmetrical PL spectrum was observed from doubly stacked InAs QDs with the nominal GaAs spacer layer thickness of 25 nm. The PL spectrum from doubly stacked InAs QDs with the nominal GaAs spacer layer thickness of 55 nm showed Gaussian-like shape with the central wavelength of 1276 nm and the FWHM of 232 nm. This PL spectrum consisted of two emission bands around 1170 and 1300 nm with almost the same intensity. These results indicate that the spectral width can be increased by controlling the spacer layer thickness in the stacked InAs QDs/GaAs structure. (C) 2010 Elsevier B.V. All rights reserved.