Electrical properties of n-GaN grown at 740℃ and 900℃ by metal-organic vapor phase epitaxy were studied in detail. According to the electrochemical capacitance-voltage measurement, it is helpful to reduce the background impurity concentration in unintendedly-doped n-GaN grown at low temperature using TEGa as Ga precursor rather than TMGa. The results of Hall effect measurement of heavily Si-doped n-GaN show that, as Si concentration increases, the electron concentration increases almost linearly, which exhibits the dopant band conducting effect, while the electron mobility decreases. Atomic force microscope and X-ray diffraction measurements show that the surface morphology and crystal quality of most samples were determined by growth temperature and Si doping level. The surface morphology of all samples had a visible change only when the doping level was much higher at the same growth temperature. On the other hand, after the samples were annealed in oxygen, the electron mobility of all the samples remained almost constant, but the electron concentration decreased when the Si concentration was larger than 6×1019 cm-3. This result indicates that in the heavily Si-doped n-GaN grown at low temperature, the annealing process could result in the formation of acceptors due to the replacement of N by Si atoms.