The mechanism bf aerosol formation during thermal decomposition of silane is investigated. To this end a Simultaneous analysis of gas-phase products of silane decomposition (disilane, trisilane, hydrogen) and the parameters of the forming aerosol particles of amorphous hydrogenated silicon is carried out. The silane loss and gaseous product concentrations are analyzed by mass-spectrometer; particle size and morphology are analyzed by transmission electron microscope. The total amount of bonded hydrogen and the relative amounts of monohydride and polyhydride groups contained in the particles are analyzed by the methods of hydrogen evolution and IR-spectroscopy. It is concluded that during the initial stages of aerosol formation, particles are mainly formed from gaseous products with a stoichiometry SinH2n. At these stages the hydrogen in particles is mainly contained as a constituent of polyhydride groups. During later stages the particles are formed from hydrogen-depleted intermediates, and the hydrogen in particles is mainly bound in monohydride groups.