This paper presents a 44-GHz MMIC medium power amplifier with a low-loss built-in linearizer using a 0.15-μm GaAs HEMT process. The proposed cold-mode HEMT linearizer can enhance the linearity of the power amplifier with a low insertion loss, a compact die-size, and zero dc consumption. These advantages make the linearizer more suitable for millimeter-wave applications. The experimental results show that the medium power amplifier output spectrum re-growth can be suppressed by 7-9 dB at 44 GHz. In addition, the EVM of the QPSK and 16-QAM modulated signal can be reduced from 4.5% to 3.7% and 10.8% to 7.4% respectively. To the best of our knowledge, this is the first attempt of using pre-distortion linearization techniques in millimeter-wave bands.