A broadband millimeter-wave (MMW) IQ demodulator is presented in this paper using standard 1P8M 0.13-μm CMOS technology. This IQ demodulator consists of two Gilbert-cell mixers, one 90° broadside coupler, and one Wilkinson power divider. This IQ demodulator has a conversion loss better than 3 dB from 35 to 50 GHz. The magnitude imbalance and image-signal rejection ratio are smaller than 1 dB and greater than 25 dBc, respectively. The 16-QAM baseband signals with 1 MHz symbol rate are used to test the digital demodulation performance. The 16-QAM baseband signals can be demodulated with an EVM of 6.3%. The chip area of this IQ demodulator is 0.9 × 1 mm2 including all testing pads.