The effect of post-growth thermal treatment of the InAs/GaAs quantum dots is investigated in this work. The photoluminescence (PL) and transmission electron microscopy (TEM) studies of samples annealed at temperatures up to 950 degrees C are presented. A complete dissolution of QDs and substantial broadening of the wetting layer (WL) can be seen from TEM. We propose that the thermally induced modification of the WL rather than QDs can be responsible for a blue-shift and narrowing of PL peaks in structures containing InAs/GaAs QDs.