The nonlinear effects causing distortion in condenser microphones are investigated and modeled with special attention paid to microphones made with silicon micromachining technology. A model of the distortion, based on the quasistatic properties, is described and solved numerically using finite differences. The results of the model show that the distortion is mainly caused by both the inverse relation between the microphone capacitance and the deflection of the diaphragm, as well as the nonlinear electrostatic forces generated by the applied dc bias voltage. The results of the model are compared with measurement results on a silicon/polyimide microphone, and good agreement is found.