We report on the growth and characterization of patterned and uniformly distributed GaN microcrystals with well-defined facets and epitaxy. The microcrystals were grown on a mask patterned by lithography. The GaN microcrystals were formed by selective-area epitaxy using metal-organic chemical-vapour deposition. The GaN microcrystals have similar sizes and shapes. Each microcrystal consists of an upper and a lower part, which are rotated by 30°. Transmission electron microscopy shows that there is a rather clear interface between the two parts of the crystal, suggesting a sudden change in the growth direction. We performed ab initio calculations for the surface energies of hexagonal GaN, and the growth morphology is explained based on surface energy considerations.