A unified analytical model for the I-V characteristics of short channel bulk nMOSFETs with (1 0 0) Si surface orientation valid for the subthreshold, linear and saturation regions is presented. In this model, the inversion layer charge is obtained considering quantum mechanical (QM) effects. The field dependent mobility variations, velocity saturation of carriers and secondary effects such as DIBL and channel length modulation have been incorporated in this model. There is a smooth transition in the current from subthreshold to above threshold and also from linear to saturation regions of operation. This results in highly continuous channel conductance (g(ds)) and transconductance (g(m)), which are important circuit parameters in small signal analysis. In addition, the result of a few benchmark tests shows that the model holds good promise for analog circuit design. The model has been implemented in SABER, a circuit simulator. The result from the model shows an excellent agreement with two-dimensional device simulator and experimental data. (C) 2009 Elsevier Ltd. All rights reserved.