There is a great interest in the development of high-power, high-efficiency, and low-cost quasicontinuous wave (QCW) diode laser bars and arrays for pumping solid state lasers. We report on the development of kW-class 88x-nm diode laser bars that are based on a bipolar cascade design, in which multiple lasers are epitaxially grown in electrical series on a single substrate and separated by low-resistance tunnel junctions with resistance as low as . QCW power of 630 W was demonstrated in a 3-mm-wide minibar with 3-mm cavity length. Peak efficiency of 61% was measured with and 14 Hz pulses, at 10°C. Further power scaling was demonstrated in a 1-cm-wide bar with 3-mm cavity length, where a record peak power of 1.8 kW was measured at 1-kA drive current. Ongoing work for further power scaling includes development of triple-junction diode laser bars.