A power-up signal generator of a semiconductor memory apparatus includes a power-up signal generating unit that includes a MOS transistor having a gate receiving a divided voltage of an external supply voltage, the power-up signal generating unit determining a level of a power-up signal according to a turn-ON state of the MOS transistor, and a bulk bias voltage generating unit that applies a bulk bias voltage to a bulk of the MOS transistor to adjust a threshold voltage of the MOS transistor, wherein the bulk bias voltage varies according to a temperature of the semiconductor memory device.