We have discovered a mechanism which can significantly reduce the dislocation density during the growth of GaN single crystals in the Na flux method. The significant reduction of the dislocation density occurs in the later stage of LPE growth, rather than solely at the seed-LPE interface for which we have already reported evidence indicating the presence of bundling dislocations. The two-step dislocation reduction is the key in achieving extremely low dislocation density using this method. We grew a two-inch GaN crystal with a thickness of 2 mm in order to confirm that the dislocation density decreases as the growth thickness increases. As a result, three-fourths of the surface area exhibited dislocation density of the order 102 cm(-2), and the FWHM of the X-ray rocking curve (XRC) measurement in (0002) face was 28 arcsec. Here, we report the two-step dislocation reduction mechanism based on LPE growth in the Na flux method. (C) 2009 Elsevier B.V. All rights reserved.