CoSi2 layers have been grown in situ on undoped polycrystalline silicon by reactive chemical vapor deposition of Co(eta (5)-C5H5)(CO)(2) at 650 degreesC, and their stability has been investigated in the temperature range from 800 to 1000 degreesC. The CoSi2 layers grown by the in situ method had grains with a strong (111) orientation, while no (111) orientation appeared in the CoSi2 layers grown by the conventional two-step method where CoSi formed first and transformed to CoSi (2). The stability of the CoSi (2) layers grown by the in situ process was improved by 100 degreesC over that of the CoSi2 layers grown by the conventional two-step process. The CoSi2 layers grown in situ on a large-grained polycrystalline silicon were stable up to 950 degreesC. The effect of stability improvement by the in situ growth was more pronounced when the grains of the polycrystalline silicon had a small size. The improved stability of the CoSi2 layers grown in situ may be mainly due to the formation of a uniform CoSi2 layer with the grains of (111) orientation.