The electrical properties of high-quality bulk GaN crystals grown by Hydride Vapor Phase Epitaxy (HVPE) were investigated. The series of samples were sliced from the same bulk crystal grown by HVPE. The crystal quality of the samples was characterized by the cathode luminescence (CL) and high resolution X-ray diffraction measurements (HRXRD), the evaluated dislocation density ranges from 2.4 x 10(6) cm(-2) to 2.3 x 10(5) cm(-2). The temperature-dependent Hall measurements were conducted and the results were analyzed theoretically. The results suggest that with low dislocation density (<= 10(6) cm(-2)) and low carrier concentration (<= 10(17) cm(-3)), the impurity concentration should play an important role in the electrical properties. With the impurity concentration decreasing, the hall mobility increases from 619 to 1160 cm(2)/(V s), and the carrier concentration decreases from 5.42 x 10(16) cm(-3) to 1.31 x 10(16) cm(-3). (C) 2015 Elsevier B.V. All rights reserved.