  The production of slow nucleons in semi-inclusive deep inelastic electron
scattering off the deuteron is investigated in the region $x \gsim 0.3$. It is
shown that within the spectator mechanism the semi-inclusive cross section
exhibits a scaling property even at moderate values of $Q^2$ ($\sim$ few
$(GeV/c)^2$) accessible at present facilities, like $CEBAF$. Such a scaling
property can be used as a model-independent test of the dominance of the
spectator mechanism itself and provides an interesting tool to investigate the
neutron structure function. The possibility of extracting model-independent
information on the neutron to proton structure function ratio from
semi-inclusive experiments is illustrated. The application of the spectator
scaling to semi-inclusive processes off complex nuclei is outlined.
