A highly integrated gain cell-type semiconductor memory is provided. A first insulator, a read bit line, a second insulator, a third insulator, a first semiconductor film, first conductive layers, and the like are formed. A projecting insulator is formed thereover. Then, second semiconductor films and a second gate insulating film are formed to cover the projecting insulator. After that, a conductive film is formed and subjected to anisotropic etching, so that write word lines are formed on side surfaces of the projecting insulator. A third contact plug for connection to a write bit line is formed over a top of the projecting insulator. With such a structure, the area of the memory cell can be 4F2 at a minimum.