Both monolayers and multilayers were obtained from a dilute solution of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] on a SiO2/Si surface after a low pressure O2 plasma treatment. A close-packed monolayer of good quality was formed on the SiO2/Si surface. The resulting self-assembled layers were characterized by goniometry, atomic force microscopy (AFM), ellipsometry and Fourier transformed infrared attenuated total reflection (FTIR-ATR) spectroscopy. An examination of the time-dependent water contact angle measurements as a function of the OTS concentration revealed rapid monolayer formation at the initial stage. The contact angle measurements showed that the surface structure of the OTS monolayer was quite resistant to environmental changes as a result of the polymerization of OTS molecules and the formation of covalent bonds between the monolayer and substrate surface. The surface was covered with islands (observed by AFM) that were in-filled to produce in a smooth surface. The FRIR-ATR spectra showed symmetric (νs(CH2)) and asymmetric (νas(CH2)) components perpendicular to the surface.