We report on quantum dot (QD) lasers made of stacked InAs dots grown by metalorganic chemical vapor deposition. Successful growth of defect-free binary InAs/GaAs QDs with high lateral density(dl⩾4×1010 cm−2)was achieved in a narrow growth parameter window. The room-temperature photoluminescence (PL) intensity is enhanced up to a factor of 3 and the PL peak width is reduced by more than 30&percent; when a thin layer ofIn0.3Ga0.7Asis deposited onto the InAs QDs. A QD laser with a single sheet of such InAs/InGaAs/GaAs QDs exhibits threshold current densities as low as 12.7 and181 A/cm2at 100 and 300 K, respectively. Lasers with threefold stacked QDs show ground-state lasing and allow for cw operation at room temperature. ©1997 American Institute of Physics.