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In this paper, a physics-based MOSFET drain thermal noise current model valid for deep submicron channel lengths was derived and verified with experiments. It is found that the well-known μQinv/L2 formula, previously derived for long channels, remains valid for short channels. Carrier heating in the gradual channel region was taken into account implicitly with the form of diffusion noise source and then impedance field method taking velocity saturation effect was used to calculate the external drain thermal noise current. The derived model was verified by experimental noise for devices with channel lengths down to 0.18 μm. Excellent agreement between measured and modeled drain thermal noise was obtained for the entire VGS and VDS bias regions.