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This invention discloses a heterojunction bipolar transistor and its fabrication method. The heterojunction bipolar transistor includes, from bottom to top, a substrate, a sub-collector region, a tunneling structure, a collector region, a base region, an emitter region, an emitter capping layer, and an ohmic contact layer. The tunneling structure comprises alternating layers of first and second conductivity types of ion doped layers. According to the heterojunction bipolar transistor and its fabrication method provided by this invention, by forming a tunneling structure composed of alternating layers of first and second conductivity types of ion doped layers between the sub-collector region and the collector region, an etch stop layer is no longer formed. The tunneling junction capacitance (Ctj) is connected in series with the collector junction capacitance (Cbc), reducing the equivalent capacitance and improving device performance.