The effects of an interposed Cu layer and a surface Cu layer on the C49-C54 TiSi2 transformation temperature were studied. For the Ti/Cu/(100)Si samples the interposed Cu layer significantly enhanced the thermal stability of C49 TiSi2. The temperature for complete C49-C54 TiSi2 transformation was raised from 710 to 735 to 750 °C with the thickness of the interposed Cu layer increasing from 0 to 1.5 to 3.5 nm, correspondingly. Cu was insoluble in C54 TiSi2. For the Cu/Ti/(100)Si samples, the surface Cu layer did not at all enhance the thermal stability of the C49 phase. In the present study, the enhanced thermal stability of C49 TiCuxSi2-x can be attributed to its reduced electron/atom ratio and larger grain size relative to those of C49 TiSi2.