We grew GaN films on r-plane sapphire substrates by pulsed sputtering and investigated their structural properties. X-ray diffraction measurements revealed that a-plane GaN grows epitaxially on r-plane sapphire with an epitaxial relation of GN [0001](GaN) // [(1) over bar 101](sapphire) and [(1) over bar 101](GaN) // [11 (2) over bar0](sapphire). In situ wafer curvature measurements revealed that the anisotropic compressive strain along [1 (1) over bar 00] and [0001](GaN) is generated during the initial stage of growth as a consequence of the anisotropy in the lattice mismatch between a-plane GaN and r-plane sapphire. We also observed that the coalescence of the GaN islands can lead to a change of stresses from compressive to tensile. (C) 2015 Elsevier B.V. All rights reserved.