An analytical model is developed for the dc characteristics of the Static Induction Transistor (SIT). The model is based on an accurate two-dimensional solution for the potential distribution in the device and is able to explain the I-V curves of the SIT in the full range of the bias condition, with a good agreement with the results of numerical simulations. The analytical model is used to study the influence of the main geometrical and physical parameters of the device on its electrical characteristics.