GaN layers of various thicknesses (40-350 mu m) were grown by hydride vapor-phase epitaxy (HVPE) on sapphire substrates and on the metal-organic chemical vapor deposition (MOCVD) grown GaN/Al2O3 templates. The quality of the grown layers on these two types of substrates is compared and studied by using diffraction interference contrast optical microscopy (DIC-OM), scanning electron microscopy (SEM), micro-Raman (mu-Raman), and high-resolution X-ray diffraction (HR-XRD) techniques. The HVPE layers grown directly on sapphire were crack-free, shiny, and transparent. These layers exhibited a smooth surface morphology, high structural quality, and a low etch pit density (EPD), i.e. 107 cm(-2). The layers grown on the MOCVD templates were also of high structural quality and exhibited good surface morphology, but suffered from different degree of cracking due to non-uniformity of strain in templates in few cases, which hindered the growth of thick layers on these templates by HVPE. The average EPD in the HVPE/MOCVD layers was of the order of middle to lower 10(8) cm(-2). (c) 2008 Elsevier B.V. All rights reserved.