Free-standing GaN wafers grown by hydride vapor phase epitaxy are typically concavely bowed. In situ and ex situ curvature measurements indicate that some strain developing at the very beginning of the epitaxial process or even in the template grown by metalorganic vapor phase epitaxy may be the origin of this bow. It can be only partly released by etching the defective back-side of the samples indicating that the strong dislocation density gradient is not the only reason for strain in free-standing GaN. (C) 2011 Elsevier B.V. All rights reserved.