The effects of the presence of charged centers of different sign on the electron mobility inn‐channel metal‐oxide‐semiconductor transistors are studied by a Monte Carlo simulation. By solving the Poisson equation for the potential fluctuations, an expression for the Coulomb‐scattering rate when there are charged centers of different sign is provided. In addition, it is shown that, when charges of different sign exist in the structure, local band‐bending fluctuations are greater, thus resulting in lower electron mobility. In contrast, since in this case the potential mean value is lower, the influence of the charged centers on the threshold voltage is lesser. The electron mobility in compensated substrates is also analyzed. ©1995 American Institute of Physics.