On charge nonconservation in FET´s

It is shown that source and drain charges are not state variables in an FET, especially for source-drain voltages near zero. This behavior, observed in the model proposed in [2], is a genuine manifestation of the physics of FET´s and is not a sign of improper behavior in a circuit simulator. However, if necessary, one may construct a model having these charges as state variables by introducing a current generator that transfers charge from source to drain internally without producing extra currents in the leads of the device.