Abstract: A submillimeter wave large-power pulse detector for 300-400 GHz frequency band is fabricated and tested. Based on the hot electron effect under high electric field, the overmoded detecting segment of the detector is composed of a waveguide WR10 and an n-type silicon detecting chip placed on the wide waveguide wall. By using lithography and electroplating techniques, the detecting chips are manufactured well with excellent ohmic contact and high dimensional precision. Submillimeter wave large-power pulses is tested and measurement of voltage standing wave ratio (VSWR) is carried out for the detector prototype. Results show that the developed detector has a response time of picoseconds-level, a relative sensitivity of about 0.46 kW-1, VSWR less than 2.4, and the maximum enduring power no less than tens of watts, agreeing well with the improved simulation results. So it satisfies the demand of the direct detect of large power pulses at submillimeter wavelength.