The formation of Si(111)–Cu interfaces has been studied systematically with photoelectron spectroscopy (hν = 21.2 eV, 16.8 eV, 10.2 eV). The samples were prepared by depositing increasing Cu thicknesses up to ten monolayers onto Si(111) held at liquid nitrogen temperature (LNT). The evolution of the photoelectron spectra due to the heating to room temperature (RT) has been studied. The coverage and temperature dependence give spectroscopic evidence of the intermixing taking place in the interface region; this causes a narrowing and a shift of the 3d Cu peak towards higher binding energies with respect to the bulk metal. In the interface intermixed region a considerable concentration gradient is present; approximately five monolayers separate the Cu-rich and the Si-rich side of the interface. This concentration gradient is higher than in the Si–Au case, and we present some speculations to explain this behavior: in this connection some preliminary LEED results on Si(111)–Cu are also used.