The synthesis and characterization of GaN thick layers are reported in this paper. The layers were prepared by sublimation sandwich method (SSM). Powder of GaN was used as the source of gallium and ammonia was used as the source of nitrogen. Sapphire with 3 mm GaN thin film grown by MOCVD was used as the substrate. The GaN layers having a current maximum size of 200 mm thickness and 10 mm  10 mm area were obtained. It is also shown that the crystals of best crystalline quality are obtained with a growth rate of 20 mm/ h. Characterization of the layers was performed using rocking curve, maps of reflection, structure refinement and SIMS. Quality of the material is good. r 2007 Elsevier B.V. All rights reserved. PACS: 71.55.Eq; 61.10.Nz