W lasers based on type-II antimonides were recently operated nearly to room temperature under the conditions of cw optical pumping. However, the development of electrically pumped mid-infrared lasers has not yet reached the same level of performance. This is largely related to the more challenging task of simultaneously optimizing the doping/transport and gain/optical properties of the devices. Here we report a demonstration of type-II mid-IR diode lasers employing W active quantum wells. Laser structures with 5 or 10 active periods sandwiched between broadened-waveguide separate confinement regions and quaternary optical cladding layers were processed into 100-µm-wide stripes, cleaved into 1-mm-long cavities, and mounted junction side down. For 0.5-1 µs pulses at a repetition rate of 200 Hz, lasing was obtained up to a maximum operating temperature of 310 K, where the emission wavelength was 3.27 µm. The threshold current densities were 110 A/cm2and 25 kA/cm2 at 78 and 310 K, respectively. The characteristic temperature, To, was 48 K for temperatures between 100 and 280 K. Operation in cw mode was obtained to 195 K, with threshold current densities of 63 A/cm2and 1.4 kA/cm2at 78 and 195 K, respectively, with To = 38 K between 78 and 195 K. Significant further improvements in the operating characteristics are expected once the optimization of the designs and fabrication procedures is complete.