[en] The ion channeling technique is applied to quantitative determinations of the depth profiles of the crystalline quality of Si-on-sapphire (SOS), and the first channeling studies of the influence of annealing temperature and ambient on the reduction of stacking faults and microtwins in as-grown SOS layers are presented. The results indicate that annealing at 1150⁰C for 24 minutes in N₂ and in N₂ + O₂ results in factors of 2 and 4 reduction in the disorder density, respectively; whereas, no appreciable reduction in disorder is obtained for 1200⁰C anneals in N₂ or in O₂ + 1% HCl. A preliminary model to explain the disorder reduction is proposed