AlGaN light-emitting diodes (LEDs) have been studied for their use as highly efficient light sources in the deep ultraviolet (DUV) region. The spontaneous and piezoelectric polarization in c-plane AlGaN, produces a strong electric field, which degrades the performance of LEDs. To overcome this polarization problem, growth on less widely used substrates, such as those with semipolar/nonpolar orientations has been carried out. However, the expected improvements have not been forthcoming for AlGaN alloys in the DUV region because of the poor crystallinity obtained. Here, we report on the improved crystallinity of semipolar AlN grown on m-plane sapphire using a high-temperature annealing process. For (10-1-3) and (11-22) AlN layers grown on m-plane sapphire, the crystal quality improved with increasing annealing temperature up to 1700 degrees C. The crystallinity of (11-22) AlN layer was further improved by further growth of AlN. A best FWHM of 280arcsec was obtained for a 3-mu m thick (11-22) AlN layer grown after high-temperature annealing.