The most common technique for measuring deposition rates in vacuum is the quartz crystal microbalance (QCM). QCMs are also employed for the determination of sputter yields; further applications are in chemistry and biology. In all these applications, the response of the resonance frequency f to temperature is important. Apart from the crystal’s sensitivity to a homogeneous temperature [the f(T) curve], the influence of the thermal stress on the frequency has to be taken into account. In contrast to standard AT-cut crystals, SC-cut (stress-compensated) crystals are insensitive to radial stress. Therefore, SC-cut crystals are used for high-precision measurements or if the power dissipated on the crystal is high (e.g., for sputter yield measurements). Nevertheless, stress effects must be taken into account if the heat source is not exactly centered. The static f(T) response and the effects of local heating, including stress effects, lead to a superposition of a fast response (within 1 s) and a slow frequency change over several minutes; the latter being related to the thermal resistance between the crystal and the crystal holder. Examples of finite-element simulations for a localized heat source will be shown and compared to experimental data of SC-cut crystals irradiated by MeV ions with up to 70 mW power, causing a temperature increase by up to 100 K.