The interfacial reaction of Nb thin films on (100) Si indicates the first phase nucleation of metal‐rich silicide and the occurrence of multiphases under certain annealing conditions. Nb3Si was identified as being the first nucleated phase at the annealing temperature of 550 °C, and subsequently Nb5Si3is found to be formed by annealing at 600 °C. The multiphases of Nb3Si, Nb5Si3, and NbSi2were observed to be formed simultaneously in the specimen annealed at 650 °C. The growth of NbSi2by the out‐diffusion of Si, which overcame the metal‐rich phase, was observed at annealing temperatures over 700 °C. ©1995 American Institute of Physics.