This paper presents linearity enhancement of CMOS device for microwave amplifier applications. The proposed method is based on a modified third-order transconductance (gm3) cancellation technique and the device is fabricated in a 0.13 μm CMOS process. For the NMOS device with the proposed gm3 cancellation technique, the third-order intermodulation distortion (IMD3) is improved by 15 dB as compared to the conventional single device. Two Ka-band CMOS amplifiers with and without the linearization are successfully evaluated. With the linearization, the measured IMD3 is enhanced by 14 dB, and the adjacent channel power ratio (ACPR) of the amplifier is improved by 7 dB for a 64-QAM modulation signal. Moreover, the linearization scheme is easily applied to the microwave amplifier and mixer designs without extra dc power consumption.