The Au/a-Si:H contact has been investigated by XPS and AES. It is found that the metal cluster occurs, at initial formation process of Au/a-Si:H interface, and after exceeding the critical Au deposition value, the Vinterdiffusion and chemical reaction of Au and Si begin and Au-Si intermixing region is formed. Furthermore, the experimental results of photoemission study confirm that Si islands are formed after annealing the interface of Au/a-Si:H.