Nickel monosilicide (NiSi) is a key material in microelectronics and its thermomechanical properties play an important role in determining the stress/strain field generated in a transistor structure. The Coefficient of Thermal Expansion (CTE) is of particular importance in the determination of such a field. As NiSi is used in microelectronics in its polycrystalline form, it becomes of particular interest to study the thermomechanical behaviour of the NiSi aggregate, considered as a unique macroscopic body. The grain orientation of a 120 nm polycrystalline NiSi film grown on single crystal silicon has been studied by means of electron diffraction, and the evaluation of the CTE tensor of the film in the wafer reference frame has been performed by weighted averaging the single grain contributions. The results clearly show the importance of orientation distribution in determining the value of the equivalent coefficient of thermal expansion of the aggregate.