Chemical modification of the Ar plasma-pretreated Si(100) surface was carried out first by UV-induced graft copolymerization with 4-vinylaniline (4-VAn) and subsequently by oxidative graft copolymerization with aniline. The graft-modified Si surface was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and electrical resistance measurements. The graft copolymerization of 4-VAn on the Si(100) surface (the VAn-g-Si(100) surface) was affected by the Ar plasma pretreatment time of the Si(100) surface, the 4-VAn monomer concentration: and the UV copolymerization time. XPS results showed that the aniline group of the grafted 4-VAn polymer could be utilised for the subsequent oxidative graft copolymerization with aniline (An). The aniline copolymer-modified VAn-g-Si(100) surface (the An-VAn-g-Si surface! exhibited protonation-deprotonation behaviour similar to that of the aniline homopolymer. The resistance of the graft-modified Si surface was in the order of 10(6) Omega /square. The AFM images revealed that the graft-modified Si surfaces had a uniform morphology. However, the roughness of the Si surface increased after the consecutive grafting processes. (C) 2000 Elsevier Science B.V. All rights reserved.