Fully integrated photonic microwave/millimeterwave (MMW) tracking generators, which include wavelengthtunable lasers, distributed feedback lasers, phase modulators, and high-speed photodiodes (PDs), are demonstrated on the heterogeneous integrated III–V-on-Si photonic platform. Two on-chip lasers are locked by an external optical phase-locked loop (OPLL), and the two-tone radio-frequency (RF) signals from the on-chip fast PDs can be photonically generated through the heterodyne-beating process between the wavelengthtunable laser and the OPLL output. Furthermore, the frequency spacing between such two-tone RF signals can be tracked by the oscillation frequency in the OPLL with a wide tunability (near dc to 10 GHz). Fast and truly continuous scanning of photogenerated MMW signals thus becomes feasible by simultaneously tuning the OPLL and the central wavelength of the tunable laser in the demonstrated photonic integrated circuit.