A physical drain current model of polysilicon thin-film transistors based on the charge-sheet model, the density of trap states and surface potential is proposed.The model uses non-iterative calculations,which are single-piece and valid in all operation regions above flat-band voltage.The distribution of the trap states,including both Gaussian deep-level states and exponential band-tail states,is also taken into account,and parameter extraction of trap state distribution is developed by the optoelectronic modulation spectroscopy measurement method. Comparisons with the available experimental data are accomplished,and good agreements are obtained. A physical drain current model of polysilicon thin-film transistors based on the charge-sheet model, the density of trap states and surface potential is proposed. The model uses non-iterative calculations, which are single-piece and valid in all operation regions above flat-band voltage. The distribution of the trap states, including both Gaussian deep-level states and exponential band-tail states, is also taken into account, and parameter extraction of trap state distribution is developed by the optoelectronic modulation spectroscopy measurement method. Comparisons with the available experimental data are accomplished, and good agreements are obtained.