We have developed a new simulation methodology for predicting shot noise intensity in Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). In our approach, shot noise in MOSFETs is calculated by employing a two dimensional device simulator in conjunction with the shot noise model of a p-n junction. The accuracy of the noise model has been demonstrated by comparing simulation results with measured noise data of p-n diodes. The intensity of shot noise in various n-MOSFET devices under various bias conditions was estimated beyond GHz operational frequency by using our simulation scheme. At DC or low-frequency region, sub-threshold current dominates the intensity of shot noise. Therefore, shot noise is independent on frequency in this region, and its intensity is exponentially depends on VG, proportional to L-1, and almost independent on VD. At high-frequency region above GHz frequency, on the other hand, shot noise intensity depends on frequency and is much larger than that of low-frequency region. In particular, the intensity of the RF shot noise is almost independent on L, VD and VG. This suggests that high-frequency shot noise intensity of MOSFETs is decided only by the conditions of source-bulk junction.