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We present a silicide nucleation process in planar metal‐silicon interfaces in terms of excess noise properties. The excess noise power spectral density has been measured in systems composed of ultrathin metal films deposited onto silicon substrates as a function of metal thickness. The metal films have been prepared by electron‐beam evaporation and rf sputtering, and structural information of the films has been obtained by using transmission electron microscopy and diffraction. Surface resistance measurements for near‐noble metal films deposited onto silicon generally show that the increase of metal thickness reduces the surface resistance of the film, which undergoes a transition from a semiconducting to a metallic state immediately prior to the onset of the first nucleation of the crystalline silicide. Results of excess noise measurements show that some of the noise parameters of the power spectral density for cobalt and nickel film on silicon have similar trends along the nucleation reaction path. A large gradual increase in noise magnitude has been observed in the prenucleation regime followed by a sudden drop below the fluctuation level for high‐resistance films after the crystallization has occurred. The noise magnitude of power spectral density is assumed to be indicative of the structural fluctuations of the interfacial layer, and thus the instability of the amorphous interfacial structure gradually grows as the metal content of the layer increases. After the electronic transition point, the chemical structure of the interfacial layer changes to a more stable long‐range‐order silicide structure. The high‐frequency exponent of the power spectral density varies from values near 3 at high film resistance to values near unity after the crystallization has occurred. The frequency exponent data may indicate that the interactions between amorphous cluster structures in the interfacial layer become stronger as- the metal content of the film increases.