A variety of undoped (nonintrinsic) hydrogenated amorphous silicon(a-Si:H)thin films was studied in greater detail using steady-state photoconductivity,&sgr;ph,subband-gap absorption,&agr;(h&ngr;), steady-state photocarrier grating (SSPG), and electron-spin-resonance (ESR) techniques both in the annealed and stabilized light soaked states. The experimental results were self-consistently modeled using a detailed numerical analysis. It was found that large differences in the optoelectronic properties of device qualitya-Si:Hthin films can only be explained using a gap state distribution which consists of positively chargedD+defect states above the Fermi level, the neutralD0defect states, and the negatively chargedD−defect states below the Fermi level. There are large differences both in the densities of neutral and charged defect states andRratios in differenta-Si:Hfilms in the annealed state. The densities of both neutral and charged defect states increased, however,Rratios decreased in the stabilized light soaked state. Very good agreement was obtained between the densities of neutral defect states measured by ESR and those derived from the numerical analysis in the stabilized light soaked state. The kinetics of the Staebler–Wronski effect was also investigated. There was no direct correlation between the decrease of steady-state photoconductivity and increase of subband-gap absorption. The self-consistent fits to wide range of experimental results obtained with the three Gaussian distributions of charged defect states imply that this model is much better representation of the bulk defect states in undoped hydrogenated amorphous silicon thin films. ©1997 American Institute of Physics.