Sulfide passivation of optically pumped GaAs/AlGaAs microdisks (at 77K) was examined. The microdisks had diameters between 2 and 10 µm and thicknesses of 0.2 µm. The layer structure was grown by organometallic vapor phase epitaxy. An ammonium sulfide solution was used for the passivation. The GaAs/AlGaAs microdisks without the sulfide treatment did not lase when optically pumped, even at the highest pump power densities of 10 kW/cm2. With sulfide treatment cw lasing was achieved with a lifetime of several seconds. A dramatic increase in the laser lifetime was obtained when the sulfide treated samples were encapsulated with silicon nitride in order to prevent loss of sulfur and surface oxidation. In addition to the lifetime increase, the laser output could be increased by nearly an order of magnitude by annealing at 400°C for 300 s or by cw operation over a period of hours at pumping powers near 10 kW/cm2.