High output power deep-ultraviolet light-emitting diodes (LEDs) are reported. First, two series devices were operated at a forward current of 350 mA. We measured powers of 45.2, 93.3, and 65.8 mW for 255, 280, and 310-nm LEDs, respectively. Next, single-chip devices with a modified epitaxial structure and electrode pattern were evaluated. Peak wavelengths, output powers, forward voltages, and external quantum efficiencies were respectively 258.0 nm, 34.8 mW, 8.25 V, 2.07% for the 255-nm LED, 282.8 nm, 40.5 mW, 5.69 V, 2.64% for the 280-nm LED, and 312.3 nm, 40.1 mW, 6.36 V, 2.89% for the 310-nm LED. The 70% lifetime of the 280-nm LED was estimated to be over 3000 h at a junction temperature of 45°C.