We have investigated the effects of reaction temperature on the characteris
tics of the directly synthesized GaN micro-crystals. For more effective syn
thesis of crystals, the bubbling technique in an atmospheric NH3 ambient wa
s used. The reaction temperature varied from 850 degrees C to 1050 degrees
C for approximately 15 hours, resulting in crystals of varing shapes and op
tical characteristics. The higher the reaction temperature increased up to
1050 degrees C, the larger the size of the crystal became, that is up to ar
ound 15 mu m. The faceted crystals such, as hexagonal and triangle polyhedr
ons, tended to form with increasing the reaction temperature. Also the samp
les grown at higher reaction temperature provided narrower emission spectra
and lower yellow band luminescence, yielding an appropriate condition for
the growth of high quality GaN micro-crystals.