Barrier height and interface states have been measured and correlated to the microstructure of the Ni silicide-Si interfaces, including the type A and type B NiSi2 and a type C NiSi. All these interfaces can be formed with near perfect structures to yield a barrier height of 0.78 eV. Less perfect interfaces formed under less than ideal conditions or with impurity incorporation deteriorate the barrier height to 0.66 eV. The density and distribution of the interface states correlate well with the structural perfection. These results suggest that the barrier height is determined primarily by the structural perfection of the interface instead of the specific type of epitaxy. © 1986.