Amorphous silicon on amorphous carbon (a-Si/a-C) multilayers was deposited by RadioFrequency (RF) sputtering. These multilayers were obtained by alternate deposition of a-C and a-Si layers, respectively from graphite and silicon targets of high purity, on crystalline silicon substrates. The RF power and the argon pressure, during the pulverization, were maintained respectively at 250W and 10-2 mbar. The annealing effects, at temperatures of 450°C and 750°C, on the deposited structures were investigated by X-ray reflectometry. The a-Si/a-C interfaces are abrupt before and after annealing at 450°C. The annealing at 750°C leads to a net decrease of both the upper a-Si layer thickness and the total multilayer thickness with a net enhancement of the interfaces reactivity. The upper silicon layer is crystallized after annealing at 750°C.