It is a common practice to extract the channel current in permeable gate MOSFETs as the average of the source and drain currents. This paper analyzes the extraction error associated to this procedure by means of theoretical calculations, measurements in a nMOS technology with 1.5 nm oxide thickness and a simple distributed model of the permeable gate MOSFET. The main dependencies of the extraction error on the bias conditions, the oxide thickness and the channel length are discussed in detail. (C) 2003 Elsevier Ltd. All rights reserved.