Corrugated horn is a kind of waveguide antenna frequently used in radio astronomy and satellite communication as a feed for its excellent performance. Due to the short wavelength, fabrication of a terahertz corrugated horn antenna becomes very difficult, which greatly limits its wide application in this frequency band. In this paper, we introduce the design of a corrugated horn antenna that works at a center frequency of 275 GHz which is fabricated using silicon platelet technology. Simulation results show that the bandwidth with better than -25 dB return loss is about 86 GHz, and the antenna gain is 19.3 dBi and while the cross-polarization level is less than -49 dB. The total weight of the horn, including integrated mounting structures for following performance testing, is only 4.2 grams.