We have studied the chemical modification and functionalization of the surface of hydrogenated amorphous silicon (a-Si:H) and silicon suboxides (a-SiOx:H) for the purpose of selective cell adhesion. The preparation of hydrophobic /hydrophilic contrast on the amorphous surfaces has been investigated systematically as a function of the oxygen content by contact angle measurements. Successful functionalization of a-Si:H by hydrosilylation with methyl acrylate is reported and analyzed by thermal desorption studies as well as enzyme linked immunosorbent assays using RGD-peptide derivatives.