The improved sub-threshold drain-source current models of a-Si:H thin-film transistors (TFTs) is demonstrated in this paper. The current-voltage (I-P) characteristics of a-Si:H TFTs are revealed in both forward and reverse sub-threshold region. The I-Vcharacteristics exhibit a strong dependence on the gate-source voltage (VGs) and the drain-source voltage (VDs). The effects of weak electron distribution and a lateral component of the electric field on the a-Si:H TFT characteristics, which are induced by VDS at both front and back interface, are considered in current model. This strong dependence of the sub-threshold current on VDs is attributed to the channel length, drain-gate overlap vicinity, and process condition. Simulated results based on the model exhibit a good agreement with measured experimental data. The proposed model and the modeling process will be very useful for practical TFTs simulation. (c) 2007 Elsevier Ltd. All rights reserved.