This paper describes a theoretical approach to understanding the impact of carrier-density-fluctuation-induced high-frequency transport noise in scaled-down MOSFETs. A theoretical expression is formulated on the basis of the charge-density conservation equation and current continuity condition. The relation between drain current noise and carrier-density fluctuation is also discussed. As scaling level is increased, the high-frequency component of normalized carrier-density fluctuation power is enhanced because the averaging effect Of fluctuation power is suppressed. It is shown that the high-frequency component of drain current noise in a 0.1-mum-channel device is more significant than that in a 1-mum-channel device.