In this work, we propose a photonic-electronic integrated circuit of a 140 GHz in-phase/quadrature (I/Q) mixer based on the GaAs-on-Si platform which is in demand of next-generation wireless networks. The mixer conversion loss is ultimately limited by the onchip power distribution network, exhibiting 7–8 dB insertion losses for the local oscillator and carrier signals with reflection losses as low as 28 dB. The circuit potentially ensures baud rates of up to 30 GHz which can be tuned. Although, the proposed integrated circuit is designed for operation at 140–150 GHz, it can be easily scaled-down for carrier frequencies of 280–300 GHz or even significantly higher. We believe that our findings should be of interest to developers of 6G wireless modules and systems.