Type-II interband cascade (IC) lasers 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 review our recent progress in InAs/GaInSb type-II IC lasers at emission wavelengths of 3.6-4 µm. These semiconductor lasers have exhibited significantly higher differential quantum efficiencies and peak powers than previously reported. Low threshold current densities (e.g., ~56 A/cm 2 at 80 K) and power efficiency exceeding 14% were observed from mesa-stripe lasers when operated in cw mode. Also, these lasers were able to operate at temperatures up to ~252 K in pulsed mode and ~142 K in cw mode. We observed slope efficiencies exceeding 1 W/A/facet, corresponding to a differential external quantum efficiency exceeding 600%, from devices at temperatures above 80 K. A peak output power of ~ 6 W/facet was observed from an IC laser at 80 K.