An analytical formula of excessive thermal noise in short-channel MOSFETs at saturation is developed following the approach used for GaAs JFET or MESFET by Statz, Haus, and Pucel. It is taken into account that the noise generated in the velocity saturation region comes from randomly generated dipole layers which propagate toward the drain contact without relaxation. Simulation of the derived formula shows that the velocity saturation region plays a crucial role in determining excessive thermal noise in short-channel MOSFETs. The proposed thermal noise formula is confirmed by the comparison to the published experimental results of high-frequency noise in the short-channel nMOSFET of channel length 0.7 mum at saturation.