In preparing an image pickup device by using hydrogen-containing amorphous silicon for a photoconductive layer, a hydrogen-containing amorphous silicon layer is first formed and is then heat-treated at 100.degree. to 300.degree. C. The image pickup characteristics of the amorphous silicon layer are highly improved by this heat treatment. For example, the lag and dark current are reduced and the signal current-target voltage characteristic is improved. Especially excellent improving effects can be obtained when amorphous silicon characterized in that (1) the hydrogen content is 5 to 30 atomic %, (2) the optical forbidden band gap is 1.30 to 1.95 eV and (3) in the infrared absorption spectrum, the component of a wave number of 2000 cm.sup.-1 is observed larger than the component of a wave number of 2100 cm.sup.-1 is subjected to the above-mentioned heat treatment. The adhesion to the substrate is enhanced, and good image pickup characteristics can be obtained.