Abstract A high-performance AlGaN/GaN-based ultraviolet (UV) light-emitting diode (LED) is successfully fabricated on sapphire substrate by metal-organic-chemical-vapor-deposition technique. Generally, a p–n junction is grown on a thick GaN layer on sapphire substrate, which results in a strong internal-absorption effect. Simultaneously, a thick AlGaN cladding layer on the GaN layer also easily produces crack. In order to avoid the internal absorption, a thick AlGaN layer is immediately introduced on a thin low-temperature GaN buffer (LT GaN buffer) instead of a thick GaN layer, which successfully avoids crack formation. However, an enhanced lattice-mismatch of AlGaN/LT GaN buffer/sapphire compared with that of GaN/sapphire might result in an enhanced dislocation density, which leads to the degraded performance of UV-LED. An AlGaN/GaN supperlattice that is applied in UV-LED instead of the thick AlGaN layer strongly decreases the dislocation density, confirmed by transmission electron microscope. Furthermore, this AlGaN/GaN supperlattice successfully avoids crack formation. Consequently, the optical power of UV-LED is greatly increased. Based on the above results, we successfully fabricate a crack-free UV-LED with a high performance.