The growth of cobalt silicides layer has been studied in Co/Ta, Co/Ta 0 . 5 W 0 . 5 and Co/W bilayers grown on Si(100) substrate. The Co and Ta-W films were deposited using thermal evaporation and sputtering techniques, respectively. All these samples were annealed at a temperature range from 400 to 1000 o C in an N 2 (80%)+H 2 (20%) environment for 60 min. The phase identification and electrical property of the annealed samples were determined by XRD and R S methods. In the Co/Ta/Si(100) system, we have obtained nearly a single crystalline CoSi 2 (200) layer with R S value of approximately 0.9 Ω/ at 900 o C. However, reappearance of Co 2 Ta phase at 1000 o C exhibits unsatisfactory thermal stability for this system. It was shown that for the Co/Ta 0 . 5 W 0 . 5 /Si(100) system, there is a reasonable thermal stability, but CoSi 2 layer was grown in a polycrystalline form with R S value of approximately 2.7 Ω/ at 1000 o C. For the Co/W/Si(100) system, we have observed nearly a single crystalline CoSi 2 (200) layer with a R S value of approximately 1.0 Ω/ at 900 o C exhibiting a good thermal stability in a temperature range from 900 to 1000 o C.