A bipolar junction transistor (BJT) includes an emitter region, a base region surrounding the emitter region, and a collector region surrounding the base region. The emitter region includes a fin structures extending along a first direction, a first metal gate extending across the fin structure along a second direction, and a second metal gate disposed in parallel with the first metal gate. A spacing between the first metal gate and the second metal gate ranges between 0.2 micrometers and 0.4 micrometers.