This paper presents the design and corresponding measurement results of a W-Band differential I-Q phase shifter in 28-nm CMOS technology. Design of CMOS active switches and passive components like a 90° hybrid realized for differential I-Q operation are shown. The phase of the RF signal can be varied from 0° to 270° in steps of 90°. The measured input and output matching are better than −10 dB, and the maximum output imbalance is 0.8 dB with a maximum phase error of 19.6° at 100 GHz. Using a 1-V supply voltage, the total power consumption is 39 mW. The die area is 0.458 mm2.