We report results of density functional theory calculations on three derivatives of the recently predicted hydrogenated silicon fullerene cluster Si20H20 using the B3PW91 hybrid exchange-correlation functional with the 6-311+G(d) basis set. The cluster has been exohedrally functionalized by replacing one of its H atoms with -CH2OH, -COOH and -CONH2. The resulting functionalized clusters have nearly the same HOMO-LUMO gaps as that of the perhydrogenated silicon fullerene leading to the possibility of developing new silicon fullerene-based molecules for medico-biological applications. The deprotonated Si20H 19(COO-) cluster displays a very large permanent dipole moment along with a strongly localized HOMO on its carboxyl group. {\textcopyright} 2003 Elsevier B.V. All rights reserved.