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 ~4 cm^-1 is achieved in the 1.35 µm range. The elimination of defects allows the stacking of QDs emitting at 1.3 µm without deterioration of their optical and structural properties and reduces the QD density in the upper sheets.