  Properties of an extended periodic Anderson model with the f-c Coulomb
interaction $\Ufc$ is studied as a model for \Ge and related compounds which is
cosidered to exhibit a sharp valence change under pressure. The problem is
treated by extending the {\it slave-boson} and large-N expansion method to
treat the present system. It is shown that, as the f-level $\epsilon_{\rm f}$
is increased relative to the Fermi level, the sharp valence change is caused by
the effect of $\Ufc$ with moderate strength of the order of the bandwith of
conduction electrons. The superconducting transition temperature $T_\rc$ due to
the valence-fluctuation exchange is estimated on the slave-boson fluctuation
approximation. In the model with spherical Fermi surface, $T_\rc$ exhibits
sharp peak as a function of $\epsilon_{\rm f}$, simulating the effect of
pressure, for the d-wave pairing channel.
