This paper demonstrates a 5.8 GHz low-power, low-flicker-noise I/Q zero-IF receiver in 0.18-um CMOS process. Passive resistive mixers and deep-n-well vertical-NPN (V-NPN) bipolar junction transistors (BJTs) as the transconductance stage of the IF amplifier are employed to improve the flicker noise problem. The passive mixer is in current mode operation and thus a step-down transformer is used at the LNA output to enhance the current gain. By carefully designing the 4:2 step-down transformer, the conversion gain of the whole zero-IF receiver performs up to 51 dB when LO power is 6 dBm, and the 3-dB bandwidth covers 5.7-6.1 GHz with the current consumption of 4.7 mA at 1.8 V supply. The flicker noise corner is 100 kHz and the noise floor is 6.5 dB. The I/Q amplitude mismatch and phase difference are below 0.05 dB and 2.5°, respectively.