A sensitive room-temperature metal-semiconductor-metal (MSM) structure is fabricated on high-resistivity silicon substrates (ρ>4 000 Ω·cm) for terahertz (THz) detection by utilizing the photoconductive effect. When radiation is absorbed by the nitrogen-rich niobium nitride, the number of free electrons and electrical conductivity increase. The detector without an attached antenna boasts a voltage responsivity of 7 058 V/W at a frequency of 310 GHz as well as small noise density of 3.5 nV/Hz0.5 for a noise equivalent power of about 0.5 pW/Hz0.5. The device fabricated by the standard silicon processing technology has large potential in high-sensitivity THz remote sensing, communication, and materials detection.