Gallium Nitride (GaN) powders were synthesized by calcining a gallium(III) sulfate salt in flowing ammonia in the temperature range 500-1100$^{circ}C$. The process of conversion of the salt to GaN was monitored by X-Ray Diffraction (XRD). The salt decomposed to ${gamma}$-Ga$_2$O$_3$ and then converted to GaN without ${gamma}$-${eta}$Ga$_2$O$_3$ phase transition. Variations in XRD patterns and weight loss of samples with temperature indicate that the conversion of ${gamma}$-Ga$_2$O$_3$ to GaN does not proceed through Ga$_2$O but stepwise via amorphous gallium oxynitride (GaO$\_$x/N$\_$y/) as intermediates. Room-temperature photoluminescence spectra of GaN powders obtained showed the emission peak at 363 nm and no yellow band.