The purpose of the present invention is to provide a terahertz detector using a field-effect transistor capable of implementing high sensitivity by exhibiting an asymmetric characteristic only with a form of a source/drain and a gate. To this end, the present invention relates to the terahertz detector using a field-effect transistor comprising: a source formed by being doped on a portion of a silicon base; a channel formed so as to encompass the source on a plane; a drain formed outside the channel; a dielectric layer formed on an upper end of the source, the channel and the drain; and a gate located at an upper end of the dielectric layer, wherein when terahertz electromagnetic waves are applied through the gate, the intensity of the electromagnetic waves is detected using a current/voltage outputted from the source and the drain.