Pulsed, optically pumped four-constituent Type-II (InAs-Ga1−xInxSb-InAs-AlSb) quantum well lasers emitting at 3.9–4.1 μm were observed to lase up to 285 K with a characteristic temperature T0 of 35 K for 170 K ≤Top≤270 K. A theoretical analysis predicts dramatic further improvements once the potential for suppressing Auger recombination is fully realized.