The reduction of the tensile stress contained in GaN layers grown oil sapphire by metalorganic vapor phase epitaxy (MOVPE) is achieved using a low density of initial GaN crystallites. The template layers exhibit a significant reduction in dislocation density, down to 5 x 10(7) cm(-2) in similar to 6 mu m thick MOVPE GaN templates. The grain size and their density are controlled during the low temperature nucleation step of GaN on sapphire. Subsequently, very thick (up to similar to 200 mu m) crack-free GaN layers were Successfully grown by hydride vapor phase epitaxy (HVPE). A direct correlation between the stress state of the GaN/sapphire template prepared by MOVPE and the critical thickness for crack appearance during HVPE growth thickening is presented. (c) 2005 Elsevier B.V. All rights reserved.