A miniature 35-110 GHz modified reflection-type BPSK modulator using a 65-nm CMOS process is presented in this paper. The core area of the modulator is only 150 × 370 μm2 due to a compact broadside coupler and a 180° hybrid used in the BPSK modulator. The BPSK modulator demonstrates a modulation bandwidth of wider than 1 GHz, an error vector magnitude (EVM) of within 10%, a dc offset of better than 15 dB, and an adjacent channel power ratio (ACPR) of better than -35 dBc The modulator is also evaluated by a bi-phase 4-level amplitude modulation scheme, and demonstrates good modulation quality with low dc offset. Therefore, it is suitable to apply to an IQ modulator design, and then the high-level modulation schemes can be performed, especially for millimeter-wave (MMW) applications. To the best authors' knowledge, this work is the highest operation frequency among all the BPSK modulator using CMOS processes.