In device‐manufacturing technology, it is important to understand why dielectric films crack. With this objective in mind, we have constructed an apparatus for measurement of thermal stresses in thin films (25–500 °C), obtained results on various reactively plasma deposited (RPD) Si‐N and CVD SiO2films, and developed a model which quantifies the cracking resistance of different types of RPD Si‐N films. Measurements were made of the coefficient of thermal expansion &agr; (T), which increases on going from SiO2→Si3N4→SiN→Si and the intrinsic stress, which is compressive for RPD Si3N4, nearly zero for thermal SiO2and tensile for RPD SiN and CVD SiO2. The cracking resistance of Si‐N film at a given temperature is functionally related to its density, intrinsic stress, thermal mismatch with Si, and the deposition temperature.