  We consider a random walk on the support of an ergodic simple point process
on R^d, d>1, furnished with independent energy marks. The jump rates of the
random walk decay exponentially in the jump length and depend on the energy
marks via a Boltzmann-type factor. This is an effective model for the
phonon-induced hopping of electrons in disordered solids in the regime of
strong Anderson localization. Under mild assumptions on the point process we
prove an upper bound of the asymptotic diffusion matrix of the random walk in
agreement with Mott law. A lower bound in agreement with Mott law was proved in
\cite{FSS}.
