Toma te dejo algo que e encontrado por google, a ver si te srive.
Punch through
Punch through in a MOSFET is an extreme case of channel length modulation where the depletion layers around the drain and source regions merge into a single depletion region. The field underneath the gate then becomes strongly dependent on the drain-source voltage, as is the drain current. Punch through causes a rapidly increasing current with increasing drain-source voltage. This effect is undesirable as it increases the output conductance and limits the maximum operating voltage of the device
te dejo el enlace
http://ece-www.colorado.edu/~bart/book/boo...pter7/ch7_7.htm][/url]