A semiconductor device includes memory blocks MB1 and MB2 and redundancy determination circuit 25 that can enter a normal operation mode that accesses either memory block MB1 or memory block MB2 and a refresh mode that simultaneously accesses both memory block MB1 and memory block MB2. In response to normal memory cell NMC that belongs to at least one of memory blocks MB1 and MB2 being replaced by redundant memory cell RMC in the refresh mode, redundancy determination circuit 25 deactivates normal cell area NCA to which normal memory cell NMC that is a source of replacement belongs, and activates redundant cell area RCA to which redundant memory cell RMC that is to be replaced belongs and normal cell area NCA to which normal memory cell NMC that is not being replaced belongs.