In this paper, we report on the characterization of a set of MOCVD grown GaN samples with a variety of structural or crystalline quality. X-ray diffraction (XRD) was used to observe the change of the crystalline structure with deposition temperature. All results show that the structure type of the GaN deposited films is sensitive to the growth temperature. Our results also revealed that a good crystalline structure of GaN films could be grown at temperatures higher than 600°C. Finally, a general picture on the correlations between the growth temperature and the GaN deposited films crystalline is reported.