A detailed experimental investigation of impact ionization in n-channel metal-oxide-semiconductor field-effect-transistors (n-MOSFET) for drain voltages close to and below the bandgap voltage is presented. The data is analyzed based on recent full-band Monte-Carlo results available in the literature. It is shown that the broadening of the tail of the electron energy distribution (EED) by electron-electron interactions (EEI) has an observable impact on hot-electron effects of n-MOSFETs of gate length of even 5 mum. Impacts of channel length scaling and gate voltage on the broadening of EED tail by EEI are also examined, and a model to explain the observed dependencies has been proposed. (C) 2003 Elsevier Science Ltd. All rights reserved.