Semiconductor structures of bipolar junction transistor (BJT) are provided. A first active region of a collection region is formed over a first P-type well region. Second and third active regions of a base region are formed over an N-type well region. A fourth active region of an emitter region is formed over a second P-type well region. The first active region includes a plurality of first fins and a plurality of first source/drain features epitaxially grown on the first fins. Each of the second and third active regions includes a plurality of second fins and a plurality of second source/drain features epitaxially grown on the second fins. The fourth active region includes a plurality of third fins and a plurality of third source/drain features epitaxially grown on the third fins. The second and third active regions are disposed on opposite sides of the fourth active region.