AbstractWe report the recent progress in type-II interband cascade (IC) lasers, For the 4.2-pm devices, lasing was observed up to 210 K, and the threshold density was only 95 A/cm2at 90 K and 284 A/cm2at 200 K. For the 4.5-μm lasers, the internal loss was only 11.6 cm−1 and the internal quantum efficiency was 460% at 90 K. We have also demonstrated the first dual-wavelength type-II IC lasers at 4.482 and 4.568 μm.