When chip-scale molding system is employed for QFP, the number of semiconductor devices available from a leadframe decreases because cavities each requires a runner portion. This problem can be overcome by employing MAP system, but use of a laminate tape increases the production cost. In through mold system, each cavity needs an ejector pin, which however makes it difficult to place a support pillar. The present application provides a manufacturing method of a semiconductor device by filling, while sandwiching a leadframe between mold dies having a matrix-state cavity group in which cavity columns obtained by linking mold cavities in series via a through gate have been placed in rows, a sealing resin in the cavities. In this method, the matrix-state cavity group has, at the cavity corner portions thereof, a support pillar having a cross-section striding over all the cavities adjacent to the cavity corner portions when viewed planarly.