An approach to generating millimeter-wave (mm-wave) signal based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) is demonstrated. In the proposed system, two phase-correlated wavelengths generated by carrier-suppressed intensity modulation are fed to an SOA as two pumps. Thanks to the degenerate FWM in the SOA, two new wavelengths that have a wavelength spacing 3 times the spacing of the two pump wavelengths are obtained. The two residual pump wavelengths are then removed by two cascaded fiber Bragg gratings (FBGs) serving as an optical notch filter. By beating the two new wavelengths at a photodetector (PD), an mm-wave having a frequency that is 6 times the frequency of the microwave drive signal is generated.