  By considering the Ginzburg-Landau model, compactified in one of the spatial
dimensions, and using a modified Matsubara formalism, we determine the
dependence of the superconducting transition temperature (T_c) of a film as a
function of its thickness (L). We show that T_c is a decreasing linear function
of L^{-1}, as has been found experimentally. The critical thickness for the
suppression of superconductivity is expressed in terms of the Ginzburg-Landau
parameters.
