A lateral DMOS transistor having a drain region which comprises a high-concentration portion with which the drain electrode is in contact and a low-concentration portion which is delimited by the channel region. In addition to the conventional source, drain, body and gate electrodes, the transistor has an additional electrode in contact with a point of the low-concentration portion of the drain region which is close to the channel. The additional electrode permits a direct measurement of the electric field in the gate dielectric and thus provides information which can be used both for characterizing the transistor and selecting its dimensions and for activating devices for protecting the transistor and/or other components of an integrated circuit containing the transistor.