Activation annealing of Si implants in metalorganic-chemical-vapor-deposition-grown GaN has been studied for use in ohmic contacts. Si was implanted in semi-insulating GaN at 100keV with doses from 5×1014to1.5×1016cm-2. Rapid thermal annealing at ∼1500°C with 100barN2 overpressure was used for dopant activation, resulting in a minimum sheet resistance of 13.9Ω/square for a dose of 7×1015cm-2. Secondary-ion-mass-spectroscopy measurements showed a post-activation broadening of the dopant concentration peak by 20nm (at half the maximum), while x-ray triple-axis ω–2θ scans indicated nearly complete implant damage recovery. Transfer-length-method measurements of the resistance of Ti/Al/Ni/Au contacts to activated GaN:Si (5×1015cm-2 at 100keV) indicated contact resistances of 0.07 and 0.02Ωmm for as-deposited and subsequently annealed contacts, respectively.