A semiconductor memory device (104) selectably connectable to an external high voltage power supply (122) is provided. The semiconductor memory device (104) includes a switch (314), a detector (316) and a timing device (318). The switch (314) is connected to external voltage supply signals and selectably couples the external voltage supply signals to memory cells (305) of the semiconductor memory device (104) for memory operations thereof. The external voltage supply signals including a high voltage signal (412) provided from the external high voltage power supply (122) and an operational voltage signal Vcc (402). The detector (316) is connected to the external voltage supply signals for generating a timer activation signal (404) in response to detecting an operational voltage power-on period. The timing device (318) signals the switch (314) to decouple the high voltage signal (412) and the operational voltage signal (402) from the memory cells (305) in response to the timer activation signal (404) and to recouple the high voltage signal (412) and the operational voltage signal (402) to the memory cells (305) a time delay interval thereafter. The time delay interval is determined in response to the high voltage signal (412).