  A resonant inelastic x-ray scattering study of the electronic structure of
the semiconductor cuprous oxide, $\rm Cu_2O$, is reported. When the incident
x-ray energy is tuned to the Cu K-absorption edge, large enhancements of the
spectral features corresponding to the electronic transitions between the
valence band and the conduction band are observed. A feature at 6.5 eV can be
well described by an interband transition from occupied states of mostly Cu 3d
charactor to unoccupied states with mixed 3d, 4s and 2p character. In addition,
an insulating band gap is observed, and the momentum dependence of the lower
bound is measured along the $\Gamma-R$ direction. This is found to be in good
agreement with the valence band dispersion measured with angle-resolved
photoemission spectroscopy.
