This paper proposed a cascaded harmonic enhanced injection-locked frequency tripler fabricated in a 40-nm CMOS process. In order to suppress the fundamental signal and the second harmonic signal, an injection-locked doubler is explored, and then the obtained ×2 frequency signal is mixed with the fundamental signal to realize the third harmonic signal and then the third harmonic signal is injected into the tank of the injection-locked frequency selection network to improve the output power. The tripler achieves a fundamental suppression over -69 dBc and a second harmonic suppression over -66 dBc. The output power over the entire locking range from 71.5 to 86.7 GHz is larger than 5.5 dBm. The chip occupies a die area of 0.25×0.35 mm2 and dissipates 20 mW of power.