Thick GaN films were grown on sapphire by the direct reaction of metallic Ga and ammonia in a conventional RF induction heated chemical vapor deposition reactor. The crystalline and optical qualities of the thick GaN were evaluated as functions of the distance between sapphire substrate and Ga source and growth temperature. For thick GaN grown at the positon of 3.5 cm away from the Ga source, the FWHM for the (0002) peak of X-ray diffraction (XRD) curve was about 684 arcsec. The growth rate of the thick GaN film was about 18㎛/h at this growth condition. The correlation between structural and optical properties of thick GaN films suggested that deep level yellow luminescence (YL) had a close relation with(1010) and (1011) planes developed in the growth. It was speculated that the emission of YL is mainly due to the formation of deep gap state in the band gap by Ga vacancy and impurities trapped at the domain boundary with (1010) and (1011) atomic facets.