The effects of Ge on the interfacial reaction between Co and poly-Si1-xGex materials were studied. Poly-Si1-xGex layers prepared at 580 degreesC by ultra-high vacuum chemical molecular epitaxy (UHVCME) system were subjected to Co silicidation at various rapid thermal annealing (RTA) temperatures ranging from 500 to 900 degreesC. From X-ray diffractometry (XRD), Co(Si1-xGex) cubic structure was formed with RTA temperature ranging from 500 to 800 degreesC for x = 0.09, while CoSi2 was formed at 900 degreesC. However, for x = 0.21, Co(Si1-yGey) persisted even after 900 degreesC RTA annealing, and CoSi2 was not found. These results indicate that Ge atoms retard the formation of CoSi2, As a result, the RTA temperature needed to obtain low sheet resistance has to be increased with increasing Ge content. Finally, p-channel metal-oxide-semiconductor (MOS) transistors with poly-Si1-xGex-gate have been successfully integrated with Co salicidation process.