The conductance of tunnel junctions formed by n-GaAs and a semitransparent metal electrode on its surface was shown to be changed by normally incident radiation with frequency below the plasma edge of n-GaAs. A spatial redistribution of the electrons due to the radiation pressure and the corresponding change in the shape of the self-consistent Schottky barrier are observed as a photoconductivity response. The comparison of the measured intensity dependence of the response to the theory has revealed an effective enhancement of the radiation field close to the n-GaAs/Me interface. The ratio Ke of the effective radiation intensity to the incident plain-wave intensity has turned out to be as large as 105. The high local electric field results in strong heating of the degenerate electron gas in the Schottky-barrier region that is mostly apparent as a photo-e.m.f. An analysis of the intensity dependence of the photo-e.m.f. is carried out involving the modification of the Schottky barrier by the ponderomotive force, the electron gas heating in Γ- and L-valleys, as well as the heating of LO phonons. The results confirm the value of Ke and allow to estimate the hot-electron temperature in Γ- and L-valleys.