In this letter, it is proposed that g _m ² /I _D , which has been used as the figure of merit (FoM) of MOSFETs for analog amplifiers, can also be used as the RF MOSFET FoM for optimizing low-noise amplifier (LNA) performance. From a simple small-signal equivalent circuit, signal gain, noise figure, and power consumption equations are derived analytically and verified with the measurement results of the fabricated LNA. The proposed g _m ² /I _D predicts the optimal bias point for the maximum LNA performance.