Partial or full nitridation of TiSi2 layers has been achieved by rapid thermal nitridation in pure ammonia. Several analytical techniques such as transmission electron microscopy, x‐ray photoemission spectroscopy, and Rutherford backscattering, have been used to study the nitridation process. It was found that a 60‐s anneal at 900 °C was sufficient to yield a 20–30 nm TiN layer on top of the TiSi2 layer, provided that the starting TiSi2 surface was free of Si or Ti oxides. Annealing at 1000 °C for 60 s, on the other hand, nitrided the entire 95‐nm TiSi2 layer. Detailed structural and chemical analysis of the samples before and after nitridation showed that the nitridation process takes place by nitrogen atoms bonding to Ti atoms and displacing the Si atoms. The dissociated Si atoms diffuse towards the TiSi2/Si interface forming an epitaxial layer of nonuniform thickness on the Si substrate. The resulting TiN layer is substantially thinner than the starting TiSi2 layer. It has a somewhat rough top surface and a very nonuniform interface with the underlying TiSi2 or Si. A small amount of Si remains on the top surface mostly in the form of Si3N4.