CVD-Si3N4 layers have been used to encapsulate Se+-implanted InP during annealing in the range 550°C to 730°C. Annealing at 700°C for about 3 min produced the best electrical properties for a dose of 1×1013 Se+ cm−2, i.e. an electrical activity of 80% and and sheet mobility of 1400 cm2V−1s−1.