White beam synchrotron radiation X-ray topography (SR-XRT) and X-ray diffraction (XRD) measurements were used to non-destructively study the defect structure of a bulk GaN wafer, grown by the ammonothermal method. SR-XRT topographs revealed high crystal quality with threading dislocation density 8.8 x 10(4) cm(-2) and granular structure consisting of large, slightly misaligned grains. The threading dislocations within grains were identified as mixed and screw type, while no pure threading edge dislocations were observed. (C) 2014 Elsevier By. All rights reserved.