  We propose a possible route to achieve high thermoelectric efficiency in
molecular junctions by combining a local chemical tuning of the molecular
electronic states with the use of semiconducting electrodes. The former allows
to control the position of the HOMO transmission resonance with respect to the
Fermi energy while the latter fulfills a twofold purpose: the suppression of
electron-like contributions to the thermopower and the cut-off of the HOMO
transmission tails into the semiconductor band gap. As a result a large
thermopower can be obtained. Our results strongly suggest that large figures of
merit in such molecular junctions can be achieved.
