The Schottky-barrier heights of Cu and its silicide Cu3Si on both n-type and p-type Si(100) have been measured in the temperature range 95295 K with the use of a current-voltage technique. X-ray photoemission spectroscopy, Rutherford backscattering, and glancing-angle x-ray diffraction were used to monitor the reaction between Cu and Si. Impurity-related energy levels in Si were determined using deep-level transient spectroscopy. Only one level was observed at 0.55 eV below the conduction-band edge upon copper deposition. Silicide formation was found to cause the disappearance of this level and also to have very little effect on the barrier height and its temperature dependence. For both the metal and the reacted silicide phase, the change in the n-type barrier height with temperature follows closely the change in the indirect energy gap in Si. The p-type barrier height does not exhibit a temperature dependence. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge. These results deviate from the predictions of models of Schottky-barrier formation based on Fermi-level pinning in the center of the semiconductor indirect band gap. Along with those Schottky barriers reported for metal-Si systems with a wide range in metal electronegativity, the present results show that the barrier height and its temperature dependence are affected by the metal.