This paper presents a miniature 38-48 GHz sub-harmonic transmitter with post-distortion linearization using a 0.15-μm GaAs HEMT process. The transmitter, which integrates a sub-harmonic mixer, a band-pass driver amplifier, and a linearizer, has a compact chip size of 2.5 mm2 with conversion gain of 7 ± 1.5 dB from 38 to 48 GHz. With the features of the sub-harmonic mixer and band-pass driver amplifier, the 2fLO leakage rejection of the transmitter is 47 dB. For the linearity of the transmitter, a post-distortion linearizer is added. After linearization, the output spectrum re-growth can be suppressed by 8 dB at 40 GHz. To keep ACPR below -35 dBc, the output power has been increased from -2 to 1 dBm, which means the linear output power lias been doubled after linearization.