The reaction between Cu and TiSi2 is studied with and without barriers, Cu being used for interconnect and TiSi2 as the gate silicide for the metal-oxide-semiconductor devices. The barriers include Ta, TiN, and W. Without a barrier, Cu reacts with TiSi2 below 300°C, forming Cu silicides. An improvement in thermal stability by 50-100°C is obtained using the barriers, with TiN/Ti being the most effective. A combined use of these barriers, with a final structure of Ta/Cu/Ta/W/TiN/Ti/TiSi 2 /Si, suppresses the Cu-TiSi2 reaction until above 600°C. The reaction mechanisms involved, and their relation with the reactions between Cu and other silicides, are discussed.