Two-dimensional (2D) analytical models for the threshold voltage and subthreshold slope of fully depleted symmetric double gate (DG) n-MOSFETs have been presented in this paper. 2D Poisson's equation has been solved with suitable boundary conditions to obtain the surface potential at the Si/SiO₂ interface. The minimum surface potential has been employed to derive analytical expressions for the threshold voltage and subthreshold slope. Also, these expressions have been modified taking into account the effect of bandgap narrowing due to heavy channel doping and quantum-mechanical effects. In addition, the 2D numerical simulation results obtained using the device simulator ATLAS for the surface potential, the threshold voltage and subthreshold slope have been presented. Further our analytical data have been compared with numerical simulation results for various DG MOSFETs, and our analytical simulation results have also been compared with reported experimental data in the literature. A good agreement is observed among the three, ensuring the validity of our present model. The proposed model is simple and makes it easy to understand the influence of physical phenomena such as quantum-mechanical effects on the electrical parameters, such as the threshold voltage, compared to other models published elsewhere.