We fabricated terahertz (THz) wave generation devices using electro-optic (EO) polymer slab waveguides and cyclo-olefin polymer (COP) clads with very small absorption loss of the THz waves based on a novel device fabrication procedure involving bonding of the poled EO polymer layer to the COP substrates. We demonstrated THz wave generation from the EO polymer slab devices using a 1.55 µm-band femtosecond fiber laser and evaluated the THz wave generation properties of the devices. Our results will lead to the development of compact, highly efficient, and ultrabroadband THz devices using EO polymers.