The interband cascade lasers (IC) represent a new class of mid-IR light sources, which take advantage of the broken-gap alignment in type-II quantum wells to reuse electrons for sequential photon emissions from serially connected active regions. Here, we describe recent progress in InAs/GaInSb type-II IC lasers at emission wavelengths of 3.8-4 µm; these semiconductor lasers have exhibited significantly higher differential quantum efficiencies and peak powers than previously reported. Also, these lasers were able to operate at temperatures up to 217 K, which is higher than the previous record (182 K) for an IC laser at this wavelength. We observed from several devices at temperatures above 80 K a slope efficiency of ∼800 mW/A per facet, corresponding to a differential external quantum efficiency of /500%. A peak optical output power exceeding 4 W/facet and peak power efficiency of /7% were observed from a device at 80 K. Also, we report the first cw operation of IC lasers.