The density of states (DOS) of hydrogenated amorphous silicon (a-Si:H) is an important issue in the study of the physics of amorphous semiconductors. In many earlier reports concerning the analysis of the field-effect conductance metal/insulator/ a-Si:H structures, namely, thin-film transistors (TFTs), the potential at the semiconductor surface apart from the gate insulator/a-Si:H interface, i.e., the rear interface, was assumed to be zero. However, in principle, as the thickness of the semiconductor film is smaller than the theoretically expected width of the space charge region, this assumption no longer holds. Hence, it is necessary to reconsider the band-bending phenomena of the a-Si:H active layers. It was found that the DOS, which was extracted previously from the field-effect conductance of the TFTs based on the assumption of the zero-potential rear interface, was appropriate only for the thick a-Si:H films. As for the thin semiconductor films, the accurate DOS can be obtained by fitting the calculated field-effect conductance, with a surmised possible DOS, to the experimentally measured data via the method developed.