Heat treatments in vacuum of Cr/a-Si:H, F structures lead to silicide formation at 450-600C. The presence of F in a-Si promotes the Cr silicide formation. The composition of the Cr silicides was found to depend on the relative thickness of the Cr and a-Si films. In the early stages of phase formation in the 400Å Cr/500Å a-Si system, with an atomic ratio of about 1:1 the first phases to appear were CrSi or CrSi2, then other silicide phases, Cr5Si3, and Cr3Si appeared. In the system with 1500Å Cr/1μm a-Si, with a surplus of Si, the dominant first phase was CrSi2, and then Cr3Si and Cr5Si3 appeared.