Joining a second supporting member to one surface of a semiconductor chip through an upper layer joining portion includes: forming, on the one surface, a pre-joining layer by pressure-sintering a first constituent member containing a sintering material on the one surface such that spaces between the plurality of protrusions are filled with the pre-joining layer and the pre-joining layer has a flat surface on a side of the pre-joining layer away from the semiconductor chip; arranging, on the flat surface, the second supporting member through a second constituent member containing a sintering material; and heating and pressurizing the second constituent member. Thereby, an upper layer joining portion is formed by the second constituent member and the pre-joining layer.