The release of hydrogen from Si1−xSnx:H (0≤x≤0.2) amorphous semiconductors prepared by reactive evaporation on substrates maintained at 77 K is monitored by effusion experiments. The effusion peaks are associated with desorption from voids. The deconvolution of these peaks allows one to deduce the different atomic configurations containing hydrogen and to determine their stability and their Gibbs free energy of desorption. ©1995 American Institute of Physics.