Static semiconductor memory device having a variable power supply voltage applied to a memory cell depending on the state in use and method of testing the same

A static semiconductor memory device comprising:

• a plurality of memory cells each having first and second storage nodes to be set at potentials of different levels from each other;
• state change detect means for detecting change of state of said memory device from the normal use mode to a testing mode;
• power supply voltage select means for applying a first power supply voltage to said plurality of memory cells when said state change detect means does not detect any change in the state from the normal use mode, and for applying a second power supply voltage to said plurality of memory cells when said state change detect means detects any change in the state from the normal use mode, said second power supply voltage is different in level from said first power supply voltage;
• wherein
• said first and second power supply voltages are for setting potential of said first or second storage node of said memory cell at a level according to the stored information;
• and
• means for testing said plurality of memory cells during application of said second power supply voltage thereto.