Ga(S2CN(CH3)(2))(3) (Ga(mDTC)(3)) nanoparticles (NPs) were prepared using ultrasonic spray method, and well mono-dispersed, with a mean particles size of 82nm. Ga(mDTC)(3) NPs changed into Ga2S3 at 300 degrees C under N-2 environment, and the spin-coated films transformed into GaN films above 700 degrees C under NH3 environment. From these results, Ga(mDTC)(3) films were transformed into -Ga2S3 films by thermal decomposition, and S elements were substituted simultaneously by N elements. In this stage, the pyrolytic GaN film underwent a recrystallization process, and a preferred direction of GaN films was mainly aligned to z-axis direction due to the lower energy surface of hexagonal structure.