The performance characteristics of InAlGaN multiple quantum well (MQW) lasers grown on sapphire and low defect density bulk AlN substrates has been compared. The group III-nitride laser heterostructures were grown on (0001) AlN and c-plane sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). Lasing was observed for optically pumped AlGaInN heterostructures in the wavelength range between 333 nm and 310 nm. A comparison of laser thresholds shows reduced threshold power densities for lasers grown on bulk AlN with threshold densities as low as 175 kW/cm2 for lasers emitting near 330 nm.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.