A unipolar semiconductor laser emitting in the mid-infrared spectral region is demonstrated. The laser scheme relies on a simple three-level system in GaAs/AlGaAs asymmetric coupled quantum wells. Population inversion between excited states is achieved by optical pumping of electrons from the ground state with aCO2laser. Long-wavelength(≈15.5 &mgr;m)laser emission is demonstrated. The laser is operated in the pulsed regime up to a temperature of 110 K and with an output peak power≈0.4 Wat 77 K. Unipolar quantum well semiconductor lasers based on this principle are capable of covering the long wavelength mid-infrared spectral region above 12 &mgr;m. ©1997 American Institute of Physics.