An improved physically-based model for deep-submicrometer SOI dynamic threshold-voltage MOSFET (DTMOS) is proposed in this paper, considering the mobile charge determined by both the forward base bias and the gate controlling for quasi-two-dimensional analysis. The alleviated dependence of the surface potential on the channel length and the drain voltage is described, as well as the unique dynamic characteristics of the threshold voltage and threshold-voltage shift for DTMOS. Key physical effects, including velocity saturation effect, mobility degradation effect and channel length modulation effect influenced by the dynamic threshold voltage, are involved in this model. The model is verified by the comparison between the model predictions, numerical results and experimental data of SOI DTMOS devices with various geometries. (C) 2003 Elsevier Science Ltd. All rights reserved.