The lattice parameters of low-defect density, undoped bulk GaN fabricated by hydride vapor phase epitaxy ͑HVPE͒ on ͑0001͒ sapphire and subsequent substrate removal, are precisely determined using high-resolution x-ray diffraction. The obtained values, c = 5.18523 Å and a = 3.18926 Å, are compared with the lattice parameters of freestanding HVPE GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by

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... he high-pressure technique and homoepitaxial GaN is made, and significant differences in the lattice parameters are found. The observed differences are discussed and a possible explanation is suggested.