In this paper, GaN films are grown by metal organic vapor phase epitaxy. Different N2 carrier gas percentages were used in the high-temperature growth process of the bulk GaN, and the dependence of sheet resistance on N2 carrier gas percentage is studied. It is found that the sheet resistance of the GaN film increases dramatically with N2 carrier gas percentage. When N2 carrier gas percentage is 50%, the sheet resistance of the GaN film is 1.1×108Ω/sq, and the surface root-mean-square roughness is as small as 0.233 nm. Secondary ion mass spectroscopy measurements reveal that the concentration of carbon and oxygen impurities is almost the same in the samples with different N2 carrier gas percentage. The density of edge-dislocation-related defects increases with N2 carrier gas percentage, while the density of screw-dislocation-related defects shows no obvious difference for all the samples. Our results indicate that the increase of the sheet resistance of GaN film is mainly due to the increase of edge threading dislocations, which act as acceptor centers in the GaN material.