High‐dose Co ion implantation in Si at elevated temperatures is used to synthesize buried CoSi2layers. It is shown that inclusions of CoSi occur in the CoSi2layer, when the stoichiometry level is exceeded at the peak of the Co distribution. These CoSi precipitates are observed prior to annealing and after a 5 s rapid thermal annealing (RTA) at 800 °C. During furnace annealing at 1000 °C or for RTA at temperatures above 900 °C, the CoSi phase transforms into CoSi2. In this communication the results of a transmission electron microscopy study of the CoSi inclusions are correlated with the Co depth profile, as determined by Rutherford backscattering spectrometry.