Electrical characteristics of thermal silicon dioxides with thickness in the range of 30-450 Å have been investigated using MOS capacitors and transistors. The general properties of thin gate-oxide FETs including subthreshold swings, channel mobilities and linear transconductances have been examined. A simple mode based on a critical electron energy for trap generation and electron scattering inside the dielectric film is proposed to explain the thick ness dependence of bulk and interface charge trapping under high field/current stress in thin oxides.