GaN micro-crystals were synthesized through the direct reaction of $NH_3$with a Ga-melt. The bubbling technique in the atmospheric $NH_3$ ambient was employed and dark-gray-colored GaN micro-crystals with various sizes ranging from 0.5~30$mu extrm{m}$ were obtained. It was confirmed that product yield increased with increasing reaction temperature. The synthesized GaN micro-crystals were characterized by using a particle size analyzer, SEM, XRD and PL. The variation of reaction temperature from $850^{circ}C$ to $1150^{circ}C$ result in morphological change and in optical characteristics of GaN micro-crystals. Especially; GaN micro-crystals synthesized at 10sec showed the highest crystallinity and low yellow band luminescence.