In this study, the effect of NH3 pre-treatment is investigated to obtain high-quality nitrogen-polar GaN grown on a SiC substrate. The GaN/AlN/C-face 4 degrees off-cut SiC structure is successfully grown with pre-treatment temperatures of 1250, 1300, and 1350 degrees C. The hillock and inversion domain density, surface roughness, and crystal quality of each sample were evaluated. As the temperature increased from 1250 degrees C to 1350 degrees C, the overall crystal quality of the N-polar GaN was greatly improved with reduced hillock and inversion domain densities and smoothed surface. The X-ray rocking curve full-width at half maximum of the (00-2) and (10-2) planes were 374 and 420 arcsec, respectively, for the pre-treatment of 1350 degrees C.