In a dynamic semiconductor memory, bit line pairs and word lines are perpendicular to each other and arranged in a matrix constituted by memory cells. Dummy cells are arranged at intersections between the bit line pairs and a pair of dummy cell word lines. The capacitance of each dummy cell is half that of the memory cell. A pre-sense amplifier and a main sense amplifier are arranged in each pair of bit lines. When data is read out from a selected memory cell, the pre-sense amplifiers are simultaneously activated to perform the pre-sensing operation. However, in the main sensing operation, only one specific main sense amplifier arranged in a certain bit line pair including the bit line connected to the selected memory cell is activated.