A memory device includes a memory cell array including a plurality of banks each including a plurality of memory cells connected to a plurality of word lines, and a row decoder block connected to the plurality of banks. In a first operation mode, the row decoder block receives a first row address and a first bank address together with an activation command and activates a word line selected by the first row address from among the plurality of word lines of a bank selected by the first bank address from among the plurality of banks. In a second operation mode, the row decoder block receives a second row address and a second bank address together with the activation command and activates a word line selected by the second row address from among the plurality of word lines of each of at least two banks of the plurality of banks.