The Monte Carlo method has been applied to an NPN silicon bipolar transistor with base and emitter widths less than O.2µm. A regional approach is adopted where the device is divided into the emitter, base, collector, and space charge regions. Only the transport of minority carriers is simulated in the submicron emitter and base regions. A comparison of the results of the Monte Carlo simulation in the base region with those obtained by solving the drift-diffusion equation shows that the latter equation predicts the carrier transport well if the absorbing boundary velocity obtained from the Monte Carlo simulation is used. However, a substantial discrepancy has been found for a very thin emitter simulation where a large retarding field is present.