The paper presents low‐frequency (flicker) noise measurements onn‐channel metal‐oxide‐semiconductor transistors with TCE (trichoroethylene), dry, thermally nitrided, or reoxidized nitrided oxides as gate dielectrics. Results show that the noise level is lowest for conventional silicon oxide with TCE treatment and highest for thermally nitrided oxide. The frequency index (&ggr;), which characterize a least‐square fit of the noise spectrum in the frequency range of 10 Hz–5 kHz to the spectrum (∝f−&ggr;), is not a constant, but fluctuates between 0.8 and 1.4 with the gate bias. In addition a trend is found that the higher the interface‐state density at the midgap of silicon, the higher the noise level. But these two quantities are not in direct proportion to each other especially for the nitrided oxide device. All these observations lead to a unique implication: in addition to interface states, the oxide traps also contribute to the flicker noise generation. Our new observations also lend support to the past speculation that the carrier number fluctuation in the conduction channel is responsible for the noise generation. However, not all the noise parameters in the present study agree well with the general predictions of the existing flicker noise models.