A 2.4-GHz direct-conversion receiver (DCR) is demonstrated using 0.18-μm CMOS technology. A passive mixer is used in this work to avoid the 1/f noise problem. Besides, a single-to-differential transformer is also used between the low-noise amplifier (LNA) and the passive mixer to perform better isolation. In addition, vertical-NPN transistors, which can be obtained in deep-n-well CMOS process without extra mask, are employed at the transconductance stage of the IF amplifiers to achieve a higher gain and lower 1/f noise than the NMOS transistors. The receiver achieves a conversion gain of 49 dB and double-sideband noise figure of 3.7 dB when the dc power consumption is 8.5 mW at a 1.8-V supply. The I/Q amplitude mismatch and phase error are below 0.3 dB and 2°, respectively, when LO frequency ranges from 2 to 3 GHz.