: Advances in deep ultraviolet (DUV) light-emitting diodes (LEDs) fabricated using wide-bandgap AlGaN-based semiconductors are described. Crystal growth techniques for wide-bandgap AlN- and AlGaN-based semiconductors have been developed and used to produce 220–350 nm-band DUV-LEDs. Significant increases in internal quantum efficacy (IQE) have been achieved for AlGaN DUV emissions by developing low threading dislocation density (TDD) AlN buffer layers on sapphire substrates. The electron injection efficiency (EIE) of the LEDs was significantly increased by introducing a multi-quantum barrier (MQB). We discuss the increase in external quantum efficiency (EQE) of AlGaN DUV-LEDs achieved by improving the IQE, as well as the EIE and light extraction efficiency (LEE).