Free-standing GaN wafers were fabricated by hydride vapor phase epitaxy (HVPE) using an in-situ self separation technique. Separation of GaN happened during the high-temperature GaN growth through thermal decomposition of the decomposable buffer layer (DBL). We optimized the growth condition of DBL, which affects not only the separation property but also the crystallinity of GaN. Free standing GaN revealed negligible residual stress, narrow (0002) omega rocking curve linewidth (67 ''), and low etch pit density (6 x 10(6) cm(-2)) as well. The carrier concentration of 4 x 10(18) cm(-3) and mobility of 150 cm(2)/V s was observed from Hall effect measurement. These results showed the Feasibility of the in-situ self-separation method to obtain high quality free-standing GaN wafer. (C) 2014 Elsevier By. All rights reserved.