  We show that Josephson junctions made of multiband semiconductors with strong
spin-orbit coupling carry a critical supercurrent $I_c$ that contains
information about the non-trivial topology of the system. In particular, we
find that the emergence and annihilation of Majorana bound states in the
junction is reflected in strong even-odd effects in $I_c$ at small junction
transparency. This effect allows for a mapping between $I_c$ and the
topological phase diagram of the junction, thus providing a dc measurement of
its topology.
