The temperature stability of metal (W, WRe, Co, Cr)‐carbon multilayers has been studied using x‐ray diffraction (&thgr;–2&thgr; and Debye–Scherrer) and electron microscopy. The results show that in all cases a crystallization occurs in the temperature range 650–750 °C. As a consequence of this crystallization, the layered structure is destroyed, the surface of the film becomes rough, and the x‐ray reflectivity is considerably reduced. These results imply that efficient cooling or new multilayer structures will have to be developed for use at high temperatures or under high x‐ray incident flux.