Abstract: A brand new type of terahertz/sub-millimeter wave detector based on InGaAs material grown on semi-insulate InP substrate was proposed with an Metal-Semiconductor-Metal(MSM) structure. High Frequency Structural Simulator(HFSS) software was firstly used to characterize the metallic planar antenna by calculating its resistance, standing-wave ratio(SWR), and the radiation pattern. Detectors with symmetrical metallic antenna were fabricated by a serious of technical process mainly including photolithograph, etching, and sputtering. Photoresponse of the detector with respect to the bias current and the modulation frequency was measured by a homemade measure system with a 0.037 5 THz Gunn oscillator terahertz source. The results show large photovoltage signal and fast respond speed (300 s) of the device. The voltage sensitivity of the detector at 0.037 5 THz reaching to 6 V/W was further obtained by the calibration of a Golay cell detector. And the noise equivalent power(NEP) at this frequency was 1.610-9 W/Hz1/2.