Editing MOSFET (section)

===Lower transconductance===
The [[transconductance]] of the MOSFET decides its gain and is proportional to hole or [[electron mobility]] (depending on device type), at least for low drain voltages. As MOSFET size is reduced, the fields in the channel increase and the dopant impurity levels increase. Both changes reduce the carrier mobility, and hence the transconductance. As channel lengths are reduced without proportional reduction in drain voltage, raising the electric field in the channel, the result is velocity saturation of the carriers, limiting the current and the transconductance.