This paper presents a 330 GHz frequency modulator. 82.5 GHz input signal is modulated by a Gilbert cell and the modulated signal is converted to 330 GHz via two cascaded push-push frequency doublers. Stacked push-push configuration is used for enhancing the output power at 330 GHz and passive Baluns with asymmetrical grounding stub is deployed to improve the power efficiency. The proposed design is fabricated using 0.13-μm SiGe BiCMOS process. The total chip area is 0.95 mm×1 mm. The DC consumption is 42.5 mW including the buffers and the input power of the 82.5 GHz carrier is -8 dBm. The proposed design demonstrates good input/output return losses through on-chip measurement and the modulated output spectrums are obtained at 330 GHz.