Experimental verification of substrate current characteristics is thoroughly carried out. VDS — VDSAT, instead of VDS, is shown to be the driving force of all hot-electron effects. A simple relationship between substrate current and VDS — VDSAT is found. This relationship provides a convenient tool to characterize the substrate current or the channel electric field, and, hence, all hot-electron effects. Measurements of ISUB/ID and VDS — VDSAT at two bias points and any one channel length are sufficient to fully characterize the substrate currents for all channel lengths VDS's and VG's for a given technology.