Dedicated to the investigation of the temperature dependence of mechanical stress in thin films (up to700 °Cin vacuum), a sensitive apparatus has been built up to measure the substrate curvature of a beam-shaped sample by deflection of a splitted laser beam from both ends. The measuring sensivity is about 0.1 MPa for a typical film thickness of 1000 nm. The long-term value over 24 h is about±0.5 MPadue to ambient-temperature drifts. The determination of absolute stress magnitudes is possible by comparative measurements between the measuring bending beam and a reference one before and after film deposition or film removal. Investigations on sputteredCu0.57Ni0.42Mn0.01films have shown that (1) the stress relaxes above300 °Cand remains nearly constant between 430 and550 °Cduring the first heating, (2) a hysteresis behavior occurs during the repeated cycles, and (3) the stress at room temperature increases a little with the cycle number. ©1998 American Institute of Physics.