  We study the superconducting order parameter near a surface with the
Bogoliubov-de Gennes formalism. For definiteness we use the attractive Hubbard
model. Near a surface, the order parameter and the density distribution exhibit
``Friedel-like'' oscillations. Although the local density of states is quite
different from that in the bulk, the energy gap in the spectrum on a surface is
almost the same as the bulk value. In the low-density limit, however, the
energy gap tends to vanish on a surface.
