By high‐frequency sputtering techniques we prepared high‐quality platinum/alumina artificial multilayers (Pt/Al2O3) with interface roughnesses below 0.2 nm and x‐ray reflectivities close to 100% at the first satellite reflection using a wavelength of 0.1542 nm. The multilayer structure remains stable up to at least 700 °C without loss in reflectivity. Further annealing causes a structural phase transition with the formation of a coherent superlattice structure, which is finally destroyed at 1000 °C. ©1995 American Institute of Physics.