A semiconductor device has multilevel memory cells, each cell storing at least three levels of data each. The multilevel memory cells are arranged so as to correspond to a physical address space, each cell storing 2.sup.n levels of data each expressed by n (n.gtoreq.2) number of bits (X1, X2, . . . , Xn). A logical address is converted into a physical address of the physical address space. A judgement is made as to whether a logical address space including the logical address matches the physical address space. When matched, the most significant bit X1 is specified by performing a single comparison operation using a reference value. The specified bit is output from one of the cells corresponding to the physical address. If not matched, the bits (X2, . . . , Xn) are specified by performing multiple comparison operations using different reference values.