We demonstrate high power AlGaN based ultraviolet light-emitting diodes (UV LEDs) with an emission wavelength of 280 nm using an asymmetric single quantum well active layer configuration on top of a high-quality AlGaN/AlN template layer grown by metalorganic chemical vapor deposition (MOCVD). An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 μm × 300 μm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current. We also demonstrate high output power operation of AlGaN-based UV LEDs at a short wavelength of 265 nm. An output power of 2.4 mW at a pulsed current of 360 mA was achieved for a single diode. A packaged array of four diodes produced 5.3 mW at 700 mA of pulsed current. The DC output power is 170 μW at 250 mA.