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/TiSi2 /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.