In this article, a scheme for fabricating low resistance Ohmic contacts to n-GaN was developed. This approach takes advantage of Ar plasma treatment and thermal annealing in forming gas ambient. As a result, the adjustment of Ar flow rate was very effective in improving the contact resistance. After proper Ar plasma treatment, the contact resistance and specific contact resistance of as-deposited Ohmic contacts were reduced to 0.362 Ω mm and 3.9×10-5 Ω cm2, respectively. Low contact resistance (0.103 Ω mm) and specific contact resistance (3.2×10-6 Ω cm2) were obtained after annealing in N2 gas ambient. By performing thermal annealing in forming gas ambient, even lower contact resistance (0.093 Ω mm) and specific contact resistance (2.6×10-6 Ω cm2) were successfully achieved, indicating that the electrical characteristics of Ohmic contacts would not be affected by the effect of hydrogen passivation of dopants in n-GaN. © 2003 American Vacuum Society.