A semiconductor memory includes a memory cell array including a plurality of memory cells arranged in rows and columns, a plurality of bit lines, each bit line connected to a corresponding column of the memory cells; a column selection circuit configured to select at least one bit line in response to a column select signal; and a read circuit configured to precharge the selected bit line in response to a precharge signal, to apply a read bias to the precharged bit line in response to a read bias provision signal, and to read data from the memory cells. A resistance level of each of the memory cells varies according to data stored therein, and the read circuit reads data from a first memory cell of the plurality of memory cells in response to the precharge signal having a first pulse width and reads data from a second memory cell of the plurality of memory cells in response to the precharge signal having a second pulse width.