By if-sputtering we have prepared high-quality metal/Al2O3 (metal: Co, Pt, W) artificial multilayers on sapphire (1120) substrates. We obtain interface roughnesses of about 0.2 nm and x-ray reflectivities of nearly 100 % at the first satellite reflection using Cu Kα radiation. The multilayer structures remain stable up to 700°C – 900°C without appreciable loss in reflectivity. Annealing causes structural changes depending on the chosen metal. Pt/Al2O3 forms a coherent superlattice structure whereas Co and W exhibit a gradual internal oxidation at the metal/Al2O3 interface. Beyond 900°C all systems are destroyed.