We studied the electrical activation of Si+ ions implanted at multiple energies (80 and 180 keV) and with a total fluence up to 2.7 × 1014 cm−2 in heteroepitaxial GaN films on sapphire. Calibrated scanning capacitance microscopy (SCM) is proposed as a method to measure the depth carrier profile after high temperature annealing (1100–1200 °C). Si electrically active fractions of 18% and 36% were obtained after low ramp rate furnace annealing at 1100 and 1200 °C, respectively. Interestingly, the dopant activation was significantly improved to 63% in the case of a rapid pre-annealing process at 1100 °C before the 1200 °C furnace annealing process. Furthermore, the ionised carrier fluence obtained by Hall measurements at room temperature exhibits a significant improvement for the 1100 °C RTA pre-annealed sample. This value is in good agreement with the ionised fluence calculated from the active Si profile …