Highly thermally stable metal silicides and methods utilizing the metal silicides in semiconductor processing are provided. The metal silicides are preferably nickel silicides formed by the reaction of nickel with substitutionally carbon-doped single crystalline silicon which has about 2 atomic % or more substitutional carbon. Unexpectedly, the metal silicides are stable to temperatures of about 900° C. and higher and their sheet resistances are substantially unaffected by exposure to high temperatures. The metal silicides are compatible with subsequent high temperature processing steps, including reflow anneals of BPSG.