It has been found that GaAs grown on GaP substrate was converted to GaN by annealing in the flow of NH 3 . Using LPE, a GaAs layer of 5 μm thickness was grown on a GaP (111)B substrate. Then the GaAs layer was annealed in the flow of 100% NH 3 for 30-60 min at 800-850°C. The GaAs layer was completely converted to GaN. X-ray diffraction measurements suggested that the GaN layer had mainly the zinc blende structure.