100 and 750 nm silver nanoclusters are fabricated on oxidized silicon and aluminum surfaces by electron beam lithography. Silver nanoclusters are characterized by atomic force microscopy, scanning electron microscopy, scanning Auger electron microscopy and high-resolution optical microscopy. The ordered structure of silver nanoclusters facilitates a thermal stability study in both reducing and oxidizing conditions. In reducing conditions, silver clusters are stable on the surfaces up to similar to 700 degrees C before evaporation. The thermal stability of silver clusters is significantly lower in oxidizing conditions. In the presence of oxygen, the silver cluster surface is oxidized and roughened < 300 degrees C. Heating above 350-400 degrees C in oxidizing conditions induces a migration of silver clusters. Micron-size and submicron-size amorphous silver clusters are formed, which spread over the oxide support. On oxidized silicon substrate, annealing treatment at 300 degrees C induces silver silicate formation or spreading of oxidized silicon support onto the silver clusters, causing a buildup of silicon on the silver cluster surface. On the oxidized aluminum surface, by contrast, no spreading or reaction of the oxide substrate with the silver clusters was detected.