We design and fabricate a good performance silicon photoconductive terahertz detector on sapphire substrates at room temperature. The best voltage responsivity of the detector is 6679V/W at frequency 300 GHz as well as low voltage noise of 3.8 nV/Hz^1/2 for noise equivalent power 0.57 pW/Hz^1/2. The measured response time of the device is about 9 μ s , demonstrating that the detector has a speed of > 110 kHz . The achieved good performance, together with large detector size (acceptance area is 3 μ m × 160 μ m ), simple structure, easy manufacturing method, compatibility with mature silicon technology, and suitability for large-scale fabrication of imaging arrays provide a promising approach to the development of sensitive terahertz room-temperature detectors.