A dynamic RAM is provided with a plurality of 1-MOSFET memory cells, each having a storage capacitor and a switching MOSFET coupled to one electrode of the storage capacitor. The other electrode of each of the storage capacitors is coupled to a switching circuit which controls the voltage which is applied to the capacitor. The switching circuit is, in turn, coupled to both a voltage generating circuit (which preferably provides a voltage of 1/2 Vcc) and a voltage supply circuit which is set to provide predetermined test voltages. Thus, by operating the switching circuit, a voltage of 1/2 Vcc can be applied to the memory cell capacitors during normal operation of the dynamic RAM, and the predetermined test voltages can be applied to the memory cell capacitors during a testing operation.