Covalent grafting of a homopolymer film onto a p-Si(100) surface was performed by use of surface electroinitiated emulsion polymerization. This polymerization method was one-step and cost-effective, and worked in the aqueous dispersed media containing both nitrobenzenediazonium (NBD) tetrafluoroborate and methyl methacrylate (MMA) monomer. NBD was reduced in the vicinity of substrate at the cut-on voltage of the pulsed voltage and was successively grafted on a Si surface, leading to a polynitrophenyl (PNP) layer. The reduction of NBD simultaneously initiated the polymerization of MMA. The resulting PMMA. macroradicals in the solution can react with the previously grafted PNP at the cutoff voltage of the pulsed voltage for thickening the polymer film. The prepared polymer layer completely covered the Si surface, as investigated by the scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. Importantly, chemical components and the thickness of the grafted polymer film were well controlled by the applied voltage and the charge flow passing through the Si electrode. X-ray photoelectron spectroscopy (XPS) measurement further confirmed the Si-C bond between the polymer layer and the Si substrate. The homopolymer film was extremely effective in protecting the underlying Si from atmospheric oxidation.