A binary phase shift keying (BPSK) transmitter with a monitoring demodulator embedded using standard 0.13-μm CMOS process is presented in this paper. Three differential switches, an RF multiplexer and a sub-harmonic VCO are applied in the circuit design. The differential switches offer the frequency-doubling function for VCO, the modulation function for the transmitter, and the demodulation function for the monitor. The measurement results show that the free-running frequency of the VCO of the chip is around 11 GHz and the doubled frequency is around 22 GHz. A continuous-wave signal is applied to test the transmitter function. The measured results show that the modulator bandwidth is wider than 6 GHz. The LO-to-RF isolation is better than 55 dB. The monitor circuit is tested to show that un-wanted signal will appear if the quality of the transmitted signal is poor. The implemented chip size is 1 × 1 mm2.