We have used neutron reflectivity and helium (3) nuclear reaction analysis to measure adsorbed amounts and concentration profiles of carboxy-terminated polystyrene chains in the melt, which are physically end-adsorbed onto the native oxide layer on silicon substrates. The excess of adsorbed chains at the substrate increases with annealing time, but more slowly than predicted by a model. We have measured the adsorption isotherm for this system. By comparison with numerical solutions of self-consistent field equations we deduce a sticking energy of 8.6 kT per molecule.