It has been shown previously that the maximum channel electric field Emin a MOSFET is the most important parameter relating to all hot-electron effects and that Emcan be represented as (VDS - VDSAT)/l, where l may be regarded as the effective length of the velocity-saturation region. The dependence of l on device geometries and process parameters is investigated in this letter. From both experiment and two-dimensional (2-D) simulation, it is found that Emhas a form of (vds vdsat)/ 0.22T1/3 oxX1/2 J, Channel length affects the saturation voltage, thus influencing the maximum channel electric field. The scaling of oxide thickness and junction depth, however, often has even greater effects on channel field. This semiempirical model of Emagrees with Emdeduced from I SUB within about 5 percent; it can predict I SUB which has been empirically correlated with hot-electron degradations.