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This paper presents the low-frequency noise (LFN) characteristics of symmetric double-gate n-FinFETs from weak to strong inversion at low drain bias. The noise-generation mechanism is investigated. The measured drain-current noise spectral density shows that LFN in the weak-inversion subthreshold region can be well described by the mobility-fluctuation model due to volume-inversion conduction behavior, which is very different from those normally observed in the bulk NMOS. The analytical expression for the drain-current noise spectral density is derived, with the Hooge parameter alphaH being extracted. In the strong-inversion linear region, the gate-voltage dependence of the room-temperature noise data agrees with the number-fluctuation model, but the slope of the frequency dependence is less than one. To determine the causes of the observed deviation from the unity slope, detailed measurements of the temperature dependence of the noise power spectra are performed, and results from two devices are presented in this paper. It is found that both the magnitude and the frequency dependence of the drain-voltage noise spectral density vary greatly in the range between 223 K and 383 K. The experimental results are compared with two models derived based on the Dutta-Horn and the McWhorter models. It is shown that the thermal-activation model of Dutta-Horn is more convincing than the latter, which shows that the noise is due to the capture and emission of carriers by oxide traps through thermal activation. The surface trap density at specific activation energy is extracted.