  We report the realization of a hybrid superconductor-quantum dot device by
means of top-down nanofabrication starting from a two dimensional electron gas
in a InGaAs/InAlAs semiconductor heterostructure. The quantum dot is defined by
electrostatic gates placed within the normal region of a planar Nb-InGaAs
quantum well-Nb junction. Measurements in the regime of strong Coulomb blockade
as well as cotunneling spectroscopy allow to directly probe the
proximity-induced energy gap in a ballistic two-dimensional electron gas
coupled to superconductors.
