Abstract-An injectorless quantum cascade laser (QCL) design using four material alloys and emitting around 8.8 µm at room temperature is presented. The coupling energy between the injection state and the upper laser level was increased compared to other injectorless designs to 10.6 meV. Devices with 85 repeats produce 2.0 W of pulsed output power per facet and an overall efficiency of 7.2% at 300 K. The threshold current density at room temperature is as low as 1.15 kA/cm 2 for an as-cleaved 4 mm long device, with a characteristic temperature of 162 K. (1) with j max and j th being the maximum and the threshold current density. N p , α m , and α i denominate the number of periods, the mirror losses and the internal losses accordingly. η tr is the differential efficiency of the laser transition. The voltage efficiency is determined by the energy per photon E ph , the voltage defect eV def , used for depletion and injection, as well as the serial resistance R s . Injectorless designs exhibit theoretically a higher efficiency, due to their smaller threshold current densities as well as their lower voltage defects. Here, one point should be noted; while reducing eV def will significantly increase the wall-plug efficiency, that occurs mostly at cryogenic temperatures. Close to and at room temperature the Manuscript