AbstractWe discuss the electrical and photo-electrical properties of monolayers of long hydrocarbon chains (alkyltrichlorosilane molecules) self-assembled on a silicon substrate. It is shown that these monolayers (<3 nm thick) act as high quality insulators : DC conductivity through the monolayers are in the 10-15 S/cm range, energy barrier heights at the silicon/monolayer interface are in the 45 eV range. Chemical surface modifications of these monolayers are reported in order to tailor their surface as well as electrical (dielectric constant) properties. Possible sub-01 μηι device applications are presented.