A recessed gate structure in a semiconductor device includes a gate electrode partially buried in a substrate, a blocking member formed in the buried portion of the gate electrode, and a gate insulation layer formed between the gate electrode and the substrate. The blocking member may effectively prevent a void or a seam in the buried portion of the gate electrode from contacting the gate insulation layer adjacent to a channel region in subsequent manufacturing processes. Thus, the semiconductor device may have a regular threshold voltage and a leakage current passing through the void or the seam may efficiently decrease.