Provided are a semiconductor device and a semiconductor device manufacturing method which can ensure the reliable contact between a plurality of semiconductor modules and a cooler and facilitate an attachment operation. The semiconductor device includes: semiconductor modules (2A to 2D) in which a circuit board having at least one or more semiconductor chips mounted thereon is sealed with a mold resin material and an attachment hole (27) is formed; main terminal plates (3A to 3C) that individually connect individual connection terminals of the plurality of semiconductor modules which are arranged in parallel; and a module storage case (4) into which the plurality of the semiconductor modules connected by the main terminal plates are inserted integrally with the main terminal plates from an opening portion (51) and which holds the plurality of semiconductor modules such that the position of the semiconductor modules can be adjusted during attachment and includes attachment insertion holes (59) facing the attachment holes of the semiconductor modules.