Reaction between Cu and PtSi is studied over 200 to 700 °C. Using structures of Cu on a preformed PtSi, and of Cu on Pt/Si, Cu-PtSi reaction is observed below 300 °C for both structures, resulting in increasing sheet resistances above this temperature. The low thermal stability of the Cu/PtSi metallurgy, compared with that of Al/PtSi, is attributed to the ready formation of Cu silicides at low temperatures. Cu3 Si and Cu4 Si are observed for both Cu/PtSi and Cu/Pt/Si structures heated to 300-400 °C. Little improvement is obtained using an 1000 Å barrier layer of Ti, W, or Cr.