A terahertz fundamental Voltage-Controlled Oscillator (VCO) with high output power in 55 nm CMOS process is proposed in this paper. The stacked structure is adopted to solve the problem of low output swing caused by the limited supply voltage of a single transistor, thereby effectively increasing the output power. Based on the unilateralization technique, a self-feeding line is embedded between the gate and drain of the core transistor to adjust the phase shift and gain between the gate and drain of the transistor to maximize the available gain of the transistor at the desired frequency, thereby increasing the power output potential of the transistor. The simulation results after extracting the parasitic parameters of the layout show that: Under a supply voltage of 2.4 V, the maximum output power of the circuit is 3.25 dBm, the minimum phase noise is -98.7 dBc/Hz at the frequency deviation of 1 MHz, and the maximum efficiency of the circuit is 8.1%. the layout area including the pad is only 0.18 mm2. This work achieves high output power with a compact area and provides a design mentality for the realization of high-power terahertz frequency fundamental wave voltage-controlled oscillators.