Semiconductor storage devices in which a plurality of semiconductor element devices having different functions are disposed in the appropriate region of the partial SOI substrate and the interface between each gate insulator and each gate electrode is formed to be the same level, and manufacturing methods thereof are disclosed. According to one aspect, there is provided a semiconductor storage device includes a first semiconductor region provided in a semiconductor substrate including a buried insulator having opening portions, a second semiconductor region without including buried insulator, a plurality of first semiconductor element devices disposed above the buried insulator, a plurality of second semiconductor element devices each disposed in a region including a region above the opening portion of the buried insulator, and a plurality of third semiconductor element devices disposed in the second semiconductor region.