  It is shown that the voltage dependence of the tunneling conductance between
two lightly doped semiconductors, which are separated by an large area
tunneling barrier, can reveal the high energy part of the Coulomb gap if the
barrier is thick enough. At the barrier thickness smaller than average distance
between impurities no Coulomb gap feature can be found. This happens because
such tunneling is sensitive to very rare shortest pairs of occupied and empty
states localized at opposite sides of the barrier, whose density of states in
this limit has no Coulomb gap. Small area tunneling contacts are also
discussed. It is shown that the tunneling conductance of a point-like contact
exponentialy grows with the applied voltage. This dependence does not permit a
direct measurement of the Coulomb gap, but indirectly has information about it.
