The reaction between Cu and Pd/Si is studied using Cu/Pd/Si structures between 200 and 600°C. The structural analyses show the reaction between Cu and Pd/Si between 200 and 300°C, with both Pd and Si diffusing into Cu, and Cu accumulating inside the Si region under the Pd2 Si layer formed. An extensive reaction between Cu and Pd2 Si is observed at 400°C, forming Cu silicides and Cu3 Pd. The instability of the Cu/Pd 2 Si metallurgy is comparable to those of Al/Pd2 Si and Cu/PtSi. In this regard, the difference in stability between the Cu/Pd/Si and Cu/Pt/Si structures is much smaller than that between the Al/Pd/Si and Al/Pt/Si ones. For the latter structures, a difference of about 100°C is observed, with or without common barrier layers, with Al/Pt/Si being the more stable one. The ready formation of both Cu silicides and Cu3 Pd contributes to the instability of the Cu/Pd/Si structure. The Cu silicide reaction is also responsible for the low thermal stability of the Cu/Pt/Si structures.