We describe the progress made in the development of type-II interband cascade lasers emitting in the midinfrared (3.8-3.9 mu m) spectral region. Three nominally similar molecular beam epitaxy growths on substrates from different vendors show qualitatively different electrical and optical properties. The devices tested show significant improvements over previously reported results with respect to differential external quantum efficiency (similar to 500%), peak power (>4 W/facet), peak power conversion efficiency (similar to 7%), maximum operating temperature (217 K), and continuous-wave operation.