A 300-GHz CMOS transmitter module with a WR-3.4 waveguide interface is presented. The CMOS transmitter is flip-chip mounted on a low-cost multilayered glass epoxy printed circuit board (PCB) and a transmission-line-to-waveguide transition with a back-short structure is built of the multilayered PCB. The measured output power and 3-dB bandwidth of the transmitter module are approximately −13.5 dBm and 10 GHz, respectively. A wireless data rate of 48 Gbit/s over 5 cm with 16-QAM is achieved using the module.