Terahertz (THz) antenna with a wide bandwidth and high Q factor is interesting for various applications, including 6G applications and THz sensing, and controlling the surface current of the antenna is known as a technique for bandwidth enhancement. The slot antenna with a metasurface is a good candidate for this aim. We have suggested a multilayer slot antenna with a metamaterial load to provide a wide bandwidth, which covers the 0.38 to 0.57 THz with a bandwidth of 40%. The metamaterial loads make various paths for the current on the surface of the antenna, which makes it possible to achieve a wider bandwidth. The proposed antenna has a gain of 4 dBi. To achieve a higher bandwidth, the dielectric silicon (Si) load is placed over the metasurface. The result shows that the height and form of the Si element can impact the bandwidth of the antenna. To modify the results of the antenna, the shape, height, and width of the dielectric load over the antenna are examined. The antenna bandwidth is enhanced, and it covers 0.371 to 0.616 THz with a 49% bandwidth. The proposed antenna is simulated with the full-wave time-domain technique of finite integrated technique.