Photoelectron spectroscopy, using a synchrotron source, has been used to study Fermi level pinning at metal-GaSe interfaces. The technique has enabled metals which react strongly with the surface to be clearly separated from those which react only weakly. Strongly interacting metals lead to stabilisation of the Fermi level at the interface, due to the generation of defect states. The non-interacting metals, in contrast, do not show pinning behaviour. For the first time shifts of the Fermi level are observed which are at least as large as those predicted by conventional theories in the Schottky limit.