Despite its promise for science and application, the electrostatic origins of the surface potential modulation caused by self-assembled monolayers (SAMs) are still not fully clear. Recently the beveled oxide method has been demonstrated as a means of measuring the electrostatic effects induced by SAM, based on a series of metal-oxide-semiconductor capacitors. In this work the beveled oxide method is expanded and applied on a series of four different alkyltrichlorosilanes monolayers. It is found that hexyltrichlorosilanes produce the largest modulation among the measured molecules. The application and limitations of the method are further discussed.