The behavior of channel avalanche breakdown in n-MOS FET’s miniaturized by isothermal constant field scaling is examined, Both a first-order analytical estimate and a rigorous two-dimensional numerical simulation of electrically wide devices are used to understand the scaling of channel breakdown. A sublinear dependence of snapback and sustaining voltages on channel length is found and explained. In practical terms, this sublinear dependence means that the relative MOS channel breakdown behavior improves for scaled-down devices. The breakdown behavior was verified against experimental data taken on a 1.3-µm n-channel device. In addition, a model is proposed for channel breakdown on unsealed devices that differ only in channel length. Copyright © 1987 by The Institute of Electrical and Electronics Engineers, Inc.