In order to reveal the relationship between the dipole moment and electric properties of organically modified semiconductor, a series of omega-functionalized alkyl monolayers on oxide-free silicon ( Si-(CH2)(10)COOH, Si-(CH2)(11)CH3, Si-(CH2)](10)COOC2H5, and Si-(CH2)(11)OH) was prepared and characterized. Electrochemical impedance measurements showed excellent insulating effects of these monolayers. It has been demonstrated that the dielectric constants of these organic monolayers are affected by the dipole moments introduced by the different terminal-groups. Solid-state electrical measurements showed that mercury \omega-functionalized alkyl monolayer \ silicon junctions exhibit molecular tunability and a clear correlation between ideality factor and the film thickness/dielectric constant ratio. The barrier height is approximately proportional to the dipole moment of the monolayer. These results augment the possibility of fine-tuning the electrical proper-ties of silicon-based microelectronic devices using functionalized organic monolayers. (c) 2006 Published by Elsevier Ltd.