Measurements of differential scanning calorimetry (DSC) in the temperature range 25 - 600 degree C were made on amorphous silicon deposited in a glow discharge system at three different substrate temperatures: T//S equals 40, 150 and 275 degree C. The results were compared with IR absorption measurements performed on as-deposited and annealed samples in order to study hydrogen evolution. The DSC thermograms revealed the existence of two exothermic processes occurring between 300 - 350 degree C and 350 - 500 degree C, respectively. The low temperature process is assigned to a local rearrangement of the amorphous network without measurable hydrogen loss; the second one originates from hydrogen evolution.