We have studied the gate finger number and gate length dependence on minimum noise figure (N Fmin) in deep sub-micrometer MOSFETs. A lowest N Fmin of 0.93 dB is measured in 0.18-μm MOSFET at 5.8 GHz as increasing finger number to 50 fingers, but increases abnormally when above 50. The scaling gate length to 0.13 μm shows larger N Fmin than the 0.18-μm case at the same finger number. From the analysis of a well-calibrated device model, the abnormal finger number dependence is due to the combined effect of reducing gate resistance and increasing substrate loss as increasing finger number. The scaling to 0.13-μm MOSFET gives higher N Fmin due to the higher gate resistance and a modified T-gate structure proposed to optimize the N Fmin for further scaling down of the MOSFET.