ABSTRACT In this thesis we deposit GaN films by magnetron rf sputtering with changes substrate temperature. The electron probe microscope analysis ( EPMA ), scanning electron microscope ( SEM ), photoluminescence measurement ( PL ) and X-ray diffraction ( XRD ) had been used to investigate these GaN films. We find GaN films crystalline quality deposit at low temperature is better then deposit at high temperature. From EPMA analysis we know higher substrate temperature lower oxygen amount of film. The ratio of Ga to N is 1.18 ~ 1.83 in average. The growth rate is about 0.30 £gm/h ~ 0.35 £gm/h in average. Thus changes substrate temperature do not influence growth rate obviously. From SEM and EDS analysis we find the roughness magnitude of films growth on sapphire substrate was smaller than the films growth on silicon substrate. We also find lower substrate temperature the roughness magnitude of films larger on silicon substrate.