Photoelectrochemical (PEC) characteristics of GaN grown by hydride vapor-phase epitaxy (HVPE) with different polarizations were studied and compared. The polar GaN used a (0001)-oriented plane and the semipolar GaN used a (20-21)-oriented plane. The photocurrent density of polar GaN exhibited a two-fold increase over that of semipolar GaN. Bulk GaN sustained water splitting up to 400 h at 0 V versus the reference electrode. To the best of our knowledge, this is the highest value reported for PEC water-splitting stability. This demonstrates the potential of GaN thin films grown by HVPE for application in large-scale solar-fuel conversion. (c) 2019 The Electrochemical Society.