The X-ray photoelectron spectroscopy (XPS) study on as deposited as well as 500 degrees C annealed Co (400 angstrom)/Si thin film synthesized by electron beam evaporation technique under UHV conditions is reported here. The XPS measurements carried out on as deposited sample rule out the possibility of any phase formation at room temperature. Whereas in 500 degrees C annealed sample the Co-2p(3/2) peak is observed at similar to 778.6 eV binding energy position, where the peak expected due to CoSi2 resides. The Auger parameters were also calculated at each step of experiment because Auger parameter is always very sensitive to changes in the chemical state of the material. The recorded spectrum on annealed sample shows Auger parameter value of similar to 1551.4 eV, which is different from that observed in the as deposited sample (similar to 1552.1 eV). The obtained results are analyzed and interpreted in terms of CoSi2 phase formation at the interface with annealing. (C) 2009 Elsevier B.V. All rights reserved.