We have studied the interface formation of Ni overlayers on cubic SiC(100) by photoemission spectroscopy with synchrotron radiation in the energy rangehν=40–140 eV. At room temperature deposition, Ni initially reacts with SiC and forms NiSi. At a nominal coverage of ∼20 Å Ni, the overlayer is metallic and the valence band spectra are identical to that of bulk Ni. The Ni/SiC(100) system is thermally stable up to ∼600 °C. The Ni overlayer reacts with the substrate to form Ni2Si at ∼800 °C. The reacted layer is inhomogeneous and consists of a mixture of SiC and Ni2Si. The reaction of Ni with SiC is quite different than that of Ni with the (111) surface of bulk Si. Ni reacts with Si(111) at 400 °C to form an epitaxial overlayer of the more Si‐rich silicide NiSi2.