A stacked semiconductor device is provided in the present invention. The stacked semiconductor device includes a first substrate and a second substrate. A first conductive pad is disposed on the first substrate. A conductive pillar contacts the first conductive pad. At least one first barrier layer is disposed inside the conductive pillar. The conductive pillar encapsulates the first barrier layer. The elastic modulus of the first barrier layer is different from the elastic modulus of conductive pillar. A second conductive pad is disposed on the second substrate. A solder bump is disposed between the first substrate and the second substrate. The solder bump electrically connects to the conductive pillar. The conductive pillar can optionally include a truncated cone.