Contact reactions between a Si substrate and thin films of Ta-V and Ti-V bilayers and codeposited alloys have been studied. The interdiffusion and silicide formation have been analyzed by Auger electron spectroscopy and x-ray diffraction. For both alloys the as-deposited films are in a single phase structure (solid solution), and metal rich compounds (M5Si 3), which are not observed for M/Si, are found at the early stages of reaction prior to the appearance of the expected stable silicides. For the Ta-V system the uniform in-depth distribution of the alloy constituents is maintained even after their silicides formation and both compounds TaSi 2 and VSi2 are mutually dissolved. The second system Ti-V, however, reveals nonuniform redistribution following the interaction with Si; enrichment with titanium silicide at the substrate interface is observed. The great affinity of Ti to form a silicide on Si is manifested in the case of the bilayer structure of Ti/V/Si when Ti atoms from the outer region penetrate through the inner V layer and form titanium silicide at the Si interface.