The thermal stability of Cu/TiN and Cu/Ti/TiN metallizations on Si, before and after annealing at 450-750 degreesC, was investigated. No change in sheet resistance and reverse-bias diode leakage current was observed for both systems after annealing up to 650 degreesC. After annealing at 750 degreesC, sheet resistance of Cu/TiN/< Si > was doubled and formation Of Cu3Si was observed by X-ray diffraction; on the contrary, the sheet resistance of the Cu/Ti/TiN/< Si > sample remains unchanged and no Cu3Si is detected. By the same annealing, leakage current density of the diodes with Cu/TiN metallization increases by three orders of magnitude, and the value for diodes with Cu/Ti/TiN metallization also increases, but only by two orders of magnitude. The additional Ti layer thus improves the metallurgical and sheet resistance stability but it cannot completely prevent the diode leakage at high temperature.