Solid state reactions in Co/amorphous-Si multilayer thin films were investigated using differential scanning calorimetry and X-ray diffraction. The results are compared with the predictions of effective driving force (EDF) and effective heat of formation (EHF) models. Amorphous silicide growth does not occur in Co/amorphous-Si multilayer thin films; this is consistent with the predictions of the EDF model. The first crystalline phase formed by solid state reaction is found to be CoSi, rather than Co2Si which is predicted by the EHF model to form first. The difference in the experimental and predicted first crystalline silicide is discussed. For Co:Si atomic concentration ratios of 2:1 and 1:2, the phase sequences are CoSi --> Co2Si and CoSi --> Co2Si --> CoSi --> CoSi2 respectively. These reactions are analyzed using the EHF diagram. The formation of CoSi and CoSi2 is controlled by nucleation and the activation energies for the formation of CoSi, Co2Si, and CoSi2 are 1.71, 2.34, and 2.79 eV respectively.