An object is to provide a semiconductor device having a novel structure, which can hold stored data even when not powered and which has an unlimited number of write cycles. A semiconductor device includes a memory cell including a widegap semiconductor, for example, an oxide semiconductor. The memory cell includes a writing transistor, a reading transistor, and a selecting transistor. Using a widegap semiconductor, a semiconductor device capable of sufficiently reducing the off-state current of a transistor included in a memory cell and holding data for a long time can be provided.