Semiconductor dice judged as good dice are stacked on a base substrate in which through holes and through hole electrodes are formed. Next, a protection layer to cover the semiconductor dice is formed. It is preferable that the protection layer is composed of a plurality of resin layers (a first resin layer and a second resin layer) that are different, in hardness from each other. Then, a conductive terminal that is connected with the through hole electrode is formed on a back surface of the base substrate. Next, the second resin layer and the base substrate are cut along predetermined dicing lines and separated into individual semiconductor devices in chip form. A process step of separation into the semiconductor devices is performed while each of the semiconductor dice is mounted on the base substrate in wafer form.