The mechanical stresses of a pure Al film and a low-thermal-expansion Al-3 at. % Ge thin film on (100) Si wafers are measured and compared in the temperature range of room temperature to 400 °C by the vibrating membrane method. The results are discussed including the comparison with those obtained by the popular wafer bending method. It was found that the chemical reaction between the Al and the Si substrate affects the mechanical stress. The relatively low stress in the Al(Ge) film is due to the interference of Ge precipitation. The relatively slow relaxation in the Al film during annealing may be caused by the dissolution of Si into Al.