Terahertz electromagnetic wave spectrum is near future candidates for widely used wireless-based systems. Its smaller wavelength than microwave offers more bandwidth, useful for high-speed data transfer and small-sized devices for more compact designs. Semiconductor-based technology has become a candidate method for providing a transducer component between electric and electromagnetic energy, an antenna. Characteristics of the dielectric material will influence the performance of an antenna designed on top of the dielectric. In such a high-frequency gap between radio waves and optics, quasi-optical has a high possibility of achieving an antenna with high radiation performance. This paper reviews previous research on a high dielectric constant silicon material designing a quasi-optical Terahertz antenna for gain enhancement purposes. We use an electromagnetic simulator of CST Microwave studio to design and simulate a considered planar dipole antenna on a high dielectric constant material of Silicon at a resonant frequency of one Terahertz. The results show that radiation energy tends to propagate into a medium with higher permittivity. Increasing the dielectric thickness and modifying its boundary surface from a flat surface into a curve makes free substrate waves, reduces internal reflections, and refracts radiation to enhance radiation gain that is useful to compensate for the high atmospheric attenuation Terahertz spectrum.