This paper presents the design and test results of a 20-GHz transmitter front-end implemented in the TSMC 0.13-µm CMOS process. The chip consists of a voltage-controlled oscillator (VCO), an RC phase splitter, and two differential switches. To realize the K-band transmitter function, the two different switches are designed to serve the purpose of frequency doubler and phase modulator, respectively. These two features are verified in the implemented chip and, as a result, the chip can serve as a transmitter front-end. The measured total current consumption of the chip core circuit is 26 mA under a DC supply voltage of 1.2 V. The chip size is 1.03 × 0.93 mm 2 .