The adhesion configurations and coverage of self-assembled monolayers (SAMs) of hydroxylated octadecyltrichlorosilane (OTS) chains on a (111) Si substrate have been studied by ab initio total energy calculations, focusing on the work function calculation for coatings with partial and full coverage. Multiple covalent attachments per molecule with the Si substrate have also been considered as possible sources of irregularities and disorder of the coating, demonstrating a relevant change in the work function. A linear dependence of the work function with respect to the surface partial dipole has been established, allowing the extrapolation of the work function to full coverage using a simple toy model. For all the adsorption configurations examined, moreover, we find that the electron work function of the coated surface is lowered with respect to the hydrogenated Si, thus increasing the hole isolation behavior. © 2012 American Chemical Society.