Capacitance and inductance expressions used for modeling critical on-chip metal interconnects. A method for calculating high frequency limit capacitances C.sub..infin. and inductances L.sub..infin. of coplanar transmission line structures over silicon substrate utilizes field based expressions derived for a single coplanar T-line structures over silicon, and coupled coplanar T lines over silicon. For coupled coplanar structures, the field lines based calculation is performed separately for odd and even modes.