This paper presents a unified analytical charge model for long channel symmetric double-gate (DG) and surrounding-gate (SGT) MOSFETs. The proposed analytical charge model continuously covers all the operation regions and achieves both computation efficiency and high accuracy. Unified intrinsic capacitance model for both DG and SGT MOSFETs is also presented for AC simulation. A detailed comparison between the analytical model and numerical solution is conducted to demonstrate the accuracy of the model. (C) 2007 Elsevier Ltd. All rights reserved.