This letter presents a broadband monolithically integrated waveguide transition module designed for operating around 300 GHz. This transition module employs waveguide WR2.8 and utilizes dipole-based transitions from waveguide to CPWG. The dipole-based transition is designed and fabricated using InP terahertz monolithic integrated circuit (TMIC) technology, so as to be directly integrated monolithically on the TMIC chip, e.g. amplifier, instead of using bond-wires. The measured results show that the insertion loss of this transition is less than 1.5 dB from 285 to 309 GHz, and return loss is better than −9 dB in the whole operation frequency band (270-330 GHz). Moreover, the dipole-based transition has a compact size that is suitable for minimal assembly.