This disclosure provides a power device, a power device assembly, and a related apparatus. The power device includes a package body and a plurality of pins. The package body includes a substrate structure, a semiconductor die, and a molded package. The semiconductor die is disposed on the substrate structure. The substrate structure includes a heat dissipation surface connectable to a heat sink. A first end of each pin is connected to the substrate structure. The molded package covers the semiconductor die and the substrate structure excluding the heat dissipation surface. A second end of each pin and the heat dissipation surface are both uncovered from the molded package. The second end of each pin includes a mounting surface connectable to a circuit board through a surface-mount technology to form an electrical connection.