  The effect of quantum confinement in the optical absorption spectra of
atomically thin {\alpha}-In2Se3 crystals is studied, observing a huge
thickness-dependent shift in the optical band gap of exfoliated {\alpha}-In2Se3
flakes. The band gap variation reported here is among the largest found in
semiconductor crystals and spans a region of the near-UV spectrum uncovered by
other 2D semiconductors.
