A semiconductor device that is less likely to be affected by a soft error is provided. The semiconductor device includes a first memory, a second memory, a processor that can be connected to the first memory and the second memory, and a selector for selectively connecting one of the first memory and the second memory to the processor. The probability of occurrence of a soft error of the first memory is higher than that of the second memory. When an error derived from a soft error is detected in the first memory, the selector connects the second memory to the processor. The semiconductor device can stably operate even when moved from an environment where a soft error is less likely to occur to an environment where a soft error is likely to occur.