A gate structure of a semiconductor memory device capable of preventing a poly void generation by forming a hard mask and maintaining a hysteresis area within a certain value. The gate structure of the semiconductor memory device includes: a gate insulation layer formed on a semiconductor substrate; a gate electrode formed on the gate insulation layer, wherein the gate electrode is formed by stacking a polysilicon layer and a metal layer; and a hard mask formed on the gate electrode, wherein a hysteresis area between the hard mask and the gate electrode materials is a equal to or less than approximately 2.times.10.sup.12 .degree. C.-dyne/cm.sup.2.