We present a study of structural changes occurring in thin amorphous silicon (a-Si). The a-Si films were deposited on single-crystalline Si substrates held at room temperature or 200 degrees C by magnetron sputtering of a Si target in pure Ar atmosphere, and therefore the films were hydrogen-free. All samples were annealed in vacuum and subsequently studied by EPR and GISAXS. A strong decrease in the dangling bonds content at lower annealing temperatures, and then an increase of it at around 550 degrees C, suggested significant structural changes. In parallel the samples were studied by GISAXS which confirmed changes at the nanometric scale attributed to voids in the material. A nice correlation of the results of the two techniques shows advantages of this approach in the analysis of structural changes in a-Si material. (c) 2006 Elsevier B.V. All rights reserved.