SEMICONDUCTOR DEVICE

摘要

An object is to provide a semiconductor device which includes a memory cell capable of holding accurate data even when the data is multilevel data. The semiconductor device includes a memory cell holding data in a node to which one of a source and a drain of a transistor whose channel region is formed from an oxide semiconductor. Note that the value of off-state current (leakage current) of the transistor is extremely small. Thus, after being set to have a predetermined value, the potential of the node can be kept constant or substantially constant by turning the transistor off. In this manner, accurate data can be stored in the memory cell.