GaN∶C films are grown on sapphire by metal-organic chemical vapor deposition (MOCVD) with different carrier gas and different CCl4 source flux. To get a high resistance (or semi-insulating) GaN, the electrical properties of GaN films influenced by CCl4 flux and carrier gas are investigated. The results show that the CCl4 flux and carrier gas influence the growth of high resistance GaN greatly. The sample A2 gets the highest sheet resistance (2.8 × 107 Ω/sq) with the CCl4 flux of 0.016 mmol/min and N2 used as the carrier gas. The atomic force microscope (AFM) test show that the samples have a flat surface morphology, the roughness is around 0.3 nm. Meanwhile, it also show that the doping C has little influence on the surface morphology. The low temperature photoluminescence (LTPL) test show that the yellow luminescence is related with edge dislocation.