  The superconducting proximity effect has played an important role in recent
work searching for Majorana modes in thin semiconductor devices. Using
transport measurements to quantify the changes in the semiconductor caused by
the proximity effect provides a measure of dynamical processes such as
screening and scattering. However, in a two terminal measurement the resistance
due to the interface conductance is in series with resistance of transport in
the semiconductor. Both of these change, and it is impossible to separate them
without more information. We have devised a new three terminal device that
provides two resistance measurements that are sufficient to extract both the
junction conductance and the two dimensional sheet resistance under the
superconducting contact. We have compared junctions between Nb and InAs and Nb
and 30% InGaAs all grown before being removed from the ultra high vacuum
molecular beam epitaxy growth system. The most transparent junctions are to
InAs, where the transmission coefficient per Landauer mode is greater than 0.6.
Contacts made with ex-situ deposition are substantially more opaque. We find
that for the most transparent junctions, the largest fractional change as the
temperature is lowered is to the resistance of the semiconductor.
