To reduce light reflection and enlarge the effective reaction surface area at the n-GaN/electrolyte interface, n-GaN epitaxial layers with naturally textured surface are utilized. The layers are combined with Cr/Au ohmic contacts on n-GaN to form working electrodes that generate hydrogen by direct photoelectrolysis of water. Although the surface reflection on the naturally textured n-GaN samples is lower than that on n-GaN epitaxial layers with flat surface, our results reveal that the photocurrent (Iph) and gas generation rates (Rgas) obtained from the naturally rough n-GaN samples are lower than those from the flat samples. The results can be attributed to the fact that the rough n-GaN surface caused by dense surface pits leads to significant recombination of photogenerated carriers with charged defects; this occurs before carriers reach the ohmic contacts, thereby resulting in lower Iph and Rgas. Related analyses have been performed and presented in this paper to initially explain the possible mechanism.