Novel mesa-type GaAs-based Blocked-Impurity-Band(BIB) detectors that can respond to the terahertz frequency have been fabricated. The key fabrication technology and the device structure are introduced in detail. Metal-Organic Chemical Vapor Deposition(MOCVD) is utilized to grow the absorption layer and the barrier layer. Low temperature testing system has been constructed and the characteristics of background response current have been investigated. At a test temperature of 3.4 K, after applying voltages scanning from -5 V to 5 V to the device, the response current has magnitude from 10-2 A to 10-6 A under 300 K background environment. In low current region, the slope of the current is relatively large. In high current area, however, the slope of the current becomes relatively small. According to the testing results, the photoelectric transport mechanisms of GaAs-based BIB detector are analyzed.