A novel design of a third-harmonic self-oscillating mixer (SOM) based on a nonlinear optimization technique, namely multi-harmonic load, has been designed. Power consumption is reduced by terminating harmonic properly, and conversion gain is optimized in the form of harmonic termination networks at dc, RF, and LO frequency, and its harmonics. In this way, a novel SOM circuit at an RF frequency of 5.79 GHz has been designed and fabricated yielding an excellent conversion gain of +11.5 dB. Gate and drain voltage supplies are -1.18V and +1.5 V, respectively and dc power consumption is about 9 mW.