Hevolution spectra were measured for hydrogenated Amorphous silicon (a-Si:H) films of varying thickness. A low temperature evolution peak at about 380 °C was determined to arise from a surface monolayer. The bulk limited main peak of the evolution spectrum arises from a very narrow range of binding energies (<0.2 eV). The evolution spectra of a-Si:H, hydrogenated polycrystalline Si, and c-Si containing platelet structures are virtually identical in both size and temperature of the various peaks. Less than 5% of the H is released in an evolution peak occurring at about 800 °C, a peak possibly due to H bound at isolated dangling bonds.