This paper presents a 120 GHz low-power wideband I/Q transmitter in a 40 nm CMOS technology for wireless chip to chip communication. The proposed transmitter consists of an up-conversion mixer, a Quadrature Injection-Locked Oscillator (QILO), gain amplifiers, and a power amplifier. The cross-coupled-capacitor topology was used to improve the conversion gain of the up-conversion mixer. By adopting a linearizer, the power amplifier achieved an output P1dB of 11 dBm. The transmitter exhibited a conversion gain of 13.5 dB, a 3 dB bandwidth of 14 GHz, and an output P1 dB of 4.5 dBm. The maximum gain mismatch between the I and Q channels in the signal bandwidth are within 2 dB. The transmitter consumed only 271 mW and its chip size is 1.51 mm(2).