The thermal decomposition of disilane (Si2H6) in a hydrogen or helium flow has been used for the deposition of hydrogenated amorphous‐silicon (a‐Si:H) films on the surface of Corning 7059 glass substrates at 450–500 °C. The reaction product consists of monosilane and trisilane in addition to the unreacted disilane and ethylsilane (the major impurity in commercial disilane). The concentration of Si2H6in the reaction mixture has been found to strongly affect the deposition rate and the photoconductivity ofa‐Si:H films. At a given Si2H6concentration, the deposition rate ofa‐Si:H films increases exponentially with temperature. At a given substrate temperature, the AM1 conductivity ofa‐Si:H films increases with increasing Si2H6concentration and approaches 10−5&OHgr; cm−1at Si2H6concentrations higher than about 4%, and the conductivity ratio in better films is about 105. The conductivities of CVDa‐Si:H films have been found to show negligible change under illumination over a period of several days. The optical band gap ofa‐Si:H films has been determined to be 1.65–1.68 eV. The doping ofa‐Si:H films with arsenic and boron has been carried out, and their activation energies determined.