A semiconductor structure including a substrate, a CMOS device and a BJT is provided. The substrate has a first side and a second side opposite to each other. The CMOS device includes an NMOS transistor and a PMOS transistor. The NMOS transistor includes a first N-type doped region and a second N-type doped region disposed in the substrate. The PMOS transistor includes a first P-type doped region and a second P-type doped region disposed in the substrate. The BJT includes a collector, a base and an emitter. The base is disposed on the first side of the substrate. The emitter is disposed on the base. A first metal silicide layer, a second metal silicide layer, and a third metal silicide layer are respectively located on the second side of the substrate and respectively disposed on the collector, the first N-type doped region, and the first P-type doped region.