Room‐temperature continuous operation (cw, 300 °K) of photopumped AlxGa1−xAs‐GaAs‐AlxGa1−xAs quantum‐well heterostructure lasers embedded in Cu under diamond windows is demonstrated. The quantum‐well heterostructures are grown by metalorganic chemical vapor deposition (MO‐CVD) and possess undoped (nd−na≲1015/cm3) or compensated (nZn∼1019/cm3,nSe∼8×1018/cm3) GaAs active layers of thicknessLz∼200 A˚.