High efficiency AlGaAs laser structures with graded index optical confinement regions and a single GaAs quantum well active region have been prepared using organometallic vapor phase epitaxy. The optimum quantum well thickness was determined to be near 50 A˚ where low internal losses are realized and the resulting threshold current densities were as low as 175 A/cm2on single ended devices with a high reflectivity coating on the rear facet. The high injected carrier levels which are associated with thin quantum well structures lead to a severe degradation in device performance if the gain required to reach lasing threshold becomes too large. If the device length, the facet reflectivities, and the operating temperature were chosen to prevent the injected carrier concentrations in the quantum well from reaching a level coincident with the onset of nonradiative carrier loss mechanisms, single ended power efficiencies exceeded 55% for room‐temperature, cw operation at 840 nm.