  Measurement of multiple Andreev reflection (MAR) in a Josephson junction made
from an InAs heterostructure with epitaxial aluminum is used to quantify the
highly transparent semiconductor-superconductor interface, indicating
near-unity transmission. The observed temperature dependence of MAR does not
follow a conventional BCS form, but instead agrees with a model in which the
density of states in the quantum well acquires an effective induced gap, in our
case 180 {\mu}eV, close to that of the epitaxial superconductor. Carrier
density dependence of MAR is investigated using a depletion gate, revealing the
subband structure of the semiconductor quantum well, consistent with
magnetotransport experiment of the bare InAs performed on the same wafer.
