Mg-doped GaN micro-crystals were prepared by using the direct reaction of liquid Ga with NH3 gas. Magnesium chloride (MgCl2) was employed as an Mg source in the growth. The growth rate and size of the Mg-doped GaN microcrystals increased with the amount of MgCl2. The micro-crystals grew with a hexagonal structure. A broad band emission peak was observed at similar to2.7 eV and its intensity increased with Mg concentration in the GaN micro-crystals. It seemed that the increase of the growth rate and the size of the micro-crystals were due to the presence of Mg and Cl species in the growth reaction. Catholuminescence also showed the blue emission at 2.85 eV due to a deep Mg-related complex. (C) 2002 Elsevier Science B.V. All rights reserved.