A semiconductor device includes a main processor, a normally-off processor, and at least one oxide semiconductor random access memory (RAM). The normally-off processor includes at least one oxide semiconductor transistor. The main processor is connected to the normally-off processor, and a clock rate of the main processor is higher than a clock rate of the normally-off processor. The oxide semiconductor RAM is connected to the normally-off processor. An operating method of the semiconductor includes backing up data from the main processor to the normally-off processor and/or the oxide semiconductor RAM.