The addition of gold nanoparticles into the semiconductors has significant effect of on the photocatalysis of the semiconductors. Gold nanoparticles can passivate the semiconductor surface, change the charge dynamics via the Fermi level equilibration, serve as the plasmonic photosensitizers and acts the surface co-catalyst. The gold nanoparticle could play more than two roles simultaneously. This presentation will discuss how to separate each role of the gold nanoparticles.