We report on the structural characterization of Mg-implanted and annealed GaN layer on Si (111). Anneals ranging from 400°C to 1100°C are performed on samples implanted with 1013 - 1015 at/cm2 Mg doses. A comparative study of the evolution of the damage in these samples as a function of annealing temperatures and implanted doses is performed by using photoluminescence (PL) and X-Ray Diffraction (XRD). For low Mg dose, the induced strain, measured via XRD, can be relaxed at relatively low temperature, i.e. 500°C, while a 1000°C anneal is required for higher dose. PL characteristics bands of Mg implanted in GaN are evidenced. Comparison of XRD and PL results show that the strain correction and the increase of the PL signal are not simultaneous. The trend in the evolution of the PL bands indicates that a higher thermal treatment would allow a better optical activation of Mg. © 2017 The Electrochemical Society.