The temperature dependence of the nonlinearity constant in pure silicon and germanium have been studied for longitudinal waves along the ⟨100⟩ axis in the temperature range 73–293 K. The estimated temperature dependence has been compared with that obtained from the experimental values of attenuation. Attenuation of 480 and 286 MHz ultrasonic waves for silicon and of 306 MHz ultrasonic waves for germanium have been evaluated, using a temperature dependent nonlinearity constantD, and compared with experimental values of attenuation available in the literature. The results are found to be in good agreement with the experimental values for silicon and germanium.