The millimeter-wave imaging approach is a promising candidate to satisfy the unmet needs of real-time biomedical imaging, such as resolution, focal area, and cost. As a part of the endeavor to make millimeter-wave imaging more feasible, this paper presents a CMOS oscillator generating a high output power at the millimeter-wave frequency range, with a high fundamental oscillation frequency. The proposed oscillator adopts a frequency-selective negative resistance topology to improve the negative transconductance and to increase the fundamental frequency of oscillation. The proposed oscillator was implemented in a 65 nm bulk CMOS process. The measured highest output power is –2.2 dBm at 190 GHz while dissipating 100 mW from a 2.8 V supply voltage.