Whether hot-carrier-induced degradation of metal-oxide-semiconductor field-effect transistors is caused by charge trapping in the oxide or interface-trap generation is a subject of considerable interest. We show that both processes take place in the hot-carrier-induced degradation. The relative importance of the two mechanisms depends on the stressing condition and the electron-trap density in the oxide. Charge trapping may be a dominant mechanism for devices with high trap density in the gate oxide. When subjected to severe degradation either by very-high-voltage stressing or by long-term stressing, the degradation of n-channel transistors seems to be mostly due to charge trapping as a result of oxide-trap generation by channel hot electrons. Under pulse stress, if the gate voltage turns off in the presence of high drain voltage, the ratio of charge trapping to interface-trap generation appears to be larger than under dc stress. This may be due to the generation of oxide traps by electron-hole recombination in the oxide. For a normal good oxide fabricated in the state-of-the-art technology under the worst-case dc bias condition or under pulse stress with inverterlike waveforms, hot-electron trapping contributes less than 10% to the device degradation and interface-trap generation is the dominant mechanism of device degradation.