A carrier-based analytic DCIV model for the long channel undoped cylindrical surrounding-gate MOSFETs is presented in this paper. It is based on an exact solution of the Poisson equation and a Pao-Sah current formulation in terms of the carrier concentration. From this model, the different dependences of the surface potential, centric potential, inversion charge and the current on the silicon body thickness and the gate oxide are elucidated analytically and then the predicted DCIV characteristics are compared with the 3D numerical simulations. The analytical results of the model presented also show in a good agreement with the 3D simulation, demonstrating the model is valid for all operation regions and traces the transition between them without any need for the fitting parameter. (c) 2006 Elsevier Ltd. All rights reserved.