A low-power high-frequency sinusoidal quadrature oscillator is presented through a new RC technique using only CMOS current mirrors. The technique is relatively simple based on (1) internal capacitances of CMOS current mirrors and (2) a resistor of a CMOS current mirror for a negative resistance. Neither external capacitances nor inductances are required. As a particular example, a 2.4 GHz-0.4 mW, 0.325-fT, CMOS sinusoidal quadrature oscillator has been demonstrated. The power consumption is very low at approximately 0.4 mW. Total harmonic distortions (THD) are less than 0.3%. The oscillation frequency is current-tunable over a range of 540 MHz or 22%. The amplitude matching and the quadrature phase matching are better than 0.035 dB and 0.15°, respectively. A figure of merit called a normalized carrier-to-noise ratio (CNRnorm) is 158.79 dBc/Hz at the 2 MHz offset from 2.46 GHz. Comparisons to other approaches are also presented.