A semiclassical Monte Carlo model is given for simulating electron transport in Si‐MOS inversion layers. The main feature of the model is that it takes into account the existence of a nonstoichiometric SiOx layer between bulk Si and the SiO2 matrix. The band‐gap in this layer is supposed to evolve linearly perpendicular to the interface from that of Si to that of SiO2. However, the band structure and electron dynamics in the SiOx layer are supposed to be dominantly that of Si. Results for drift velocity in the hot carrier regime are compared with the most recent experimental data. The spatial evolution of the carrier concentration near the interface is also investigated. It is found that the carriers may penetrate into the SiOx layer.