An excess-noise current in CMOS Magnetic Sensitive Field Effect Transistor (MAGFET) split-drain transistors is investigated, and a new noise model is proposed. The model is based on the existence of the transversal noise current that stems from the inversion charge layer in the MOS transistor channel. This excess-noise current, along with the one predicted by the classical MOS transistor, produces the total split-drain noise current. Noise spectral density measurements were carried out to verify the proposed model for split-drain MAGFETs manufactured in 0.8 and 0.35-mu m CMOS, with an equal geometric aspect ratio of 10 mu m/10 mu m.544885887