Strained quantum‐well lasers emitting at 4.5 μm have been fabricated. The laser structure, grown on a GaSb substrate by molecular beam epitaxy, consists of compressively strained InAsSb active layers and tensile‐strained InAlAs barrier layers, surrounded by AlAsSb cladding layers. Under electrical injection, the laser exhibited pulsed operation up to 85 K, with threshold current density of 350 A/cm2 at 50 K. Under optical pumping, the laser operated pulsed up to 144 K, with peak power at 95 K of 0.54 W.