The initial stages of formation of the Ir/Si interface were investigated with ultraviolet and x-ray photoelectron spectroscopy. It was found that submonolayer coverages of iridium change the (2×1) reconstruction of the clean silicon surface and increase the band bending. With increasing coverage a bilayer structure forms consisting of an interfacial layer of IrSi-like silicide and an overlayer of pure iridium. The Schottky barrier is fully developed after deposition of the first monolayer of iridium. By annealing a thin film of iridium deposited on silicon in UHV in the temperature range of 4001100°C we demonstrate the consecutive formation of three silicide compounds in the sequence IrSi, IrSix (x1.6), and IrSi3 and the concomitant transitions from metallic to semiconducting and semiconducting to metallic behavior. Finally, we show that the barrier heights of the iridium silicides on silicon do not obey the simple Schottky model and compare our photoelectron results with current theoretical models of the Schottky barrier.