Through a tight-binding rigid-band approach we show that changes in the relative stability of theC54,C49,andC40phases ofTiSi2,with electrons per atom ratio, are produced by the corresponding differences in the electronic density of states at the Fermi level. In particular, by increasing this ratio the stable phase evolves fromC49toC54,and then toC40.Our microscopic model provides a straightforward interpretation of very recent experimental findings concerning the sizeable variations in the transition temperature betweenC49andC54TiSi2in the presence of Al or Mo layers. ©1998 American Institute of Physics.