1. A power-up signal generator for a semiconductor memory device, comprising: a power-up detector for generating a power-up detection signal by an external power supply voltage; deep power down power-up signal generator for generating a deep power down power-up signal in response to the power-up detection signal; power-up signal generator for generating a power-up signal in response to the power-up detection signal; and power-up controller for determining whether or not enable the power-up signal in a deep power down entry.