For the substrate coupling digital noise-free monolithic 3-dimensional (M3D) mixed-signal integrated circuit (IC), we have demonstrated InGaAs HEMTs on Si CMOS. Bottom digital circuits were fabricated by 180 nm standard Si CMOS and top RF InGaAs HEMTs were fabricated on Si CMOS by wafer bonding-based layer transfer and low-processing temperature of 300 ℃ or less. As a result, top InGaAs HEMTs exhibit f T and f MAX of 448 and 213 GHz without any degradation in the bottom Si CMOS. It is the record-high f T ever reported by M3D RF transistors. Furthermore, for the first time, we have successfully demonstrated that the influence of substrate digital noise can be eliminated by integrating the analog and digital circuits in the M3D platform.