Annealing of InGaAs quantum dots (QDs) fabricated by metal-organic chemical vapour deposition and covered with a very thin GaAs cap layer completely eliminates large dislocated InGaAs clusters and remarkably improves the optical properties of the structures. A modal gain of similar to 4 cm(-1) is achieved in the 1.35 mu m range. The elimination of defects allows the stacking of QDs emitting at 1.3 mu m without deterioration of their optical and structural properties and reduces the QD density in the upper sheets.