AbstractAn analysis of the threshold current densities and differential slope efficiencies in interband cascade lasers with type-II active regions revealed lower Auger recombination rates than anticipated theoretically or using the data from prior experiments. Furthermore, a new design of the waveguide yielded room-temperature internal losses as low as ≈6 cm−1. The combination of these advances with improvements to the processing of narrow ridges has led operation up to 335 K in continuous-wave mode for devices emitting at 3.3–3.7 μm. An 8.7 μm-wide ridge without facet coatings produced up to 23 mW of cw power at 300 K, and displayed a maximum wall-plug efficiency of 2.0%.