Abstract: Systematic investigations of photoelectrochemical behavior between Au nano-particle modified n- and p-GaN were reported in this study. With Au nanoparticles sputtered on the surface, strong Fermi level pinning caused by the creation of metal induced gap states alters the behavior of electrolyte/GaN interface. Under illumination, the photocurrent of p-GaN at zero bias exhibited 25 times enhancement, whereas that of n-GaN showed slight decrease. The overall hydrogen generation efficiency of p-GaN in HCl solution was increased from 0.02% to around 0.59%. The enhancement can be attributed to the different energy shift of the surface band edge at the interface according to the doping of GaN.