Wavelength, material and dimension are crucial elements to consider when modelling a waveguide. In this research paper, a hybrid plasmonic Terahertz (THz) waveguide is constructed at around 3 THz using Gallium Arsenide (GaAs), a high-index material is embedded in a low-index material to confine THz waves efficiently. The effective mode area, propagation length, effective refractive index and figure of merit have been fully examined using the finite element method utilizing the Comsol multiphysics software tool. The results of the proposed THz waveguide exhibit a high effective refractive index of 3.14, long propagation length of 910 μm, large effective mode area of 1.9 μm2 and high figure of merit of 944 at around 3 THz.