Embodiments relate to a manufacturing method of a flash memory device which improves electrical characteristics by reducing or preventing void generation. A manufacturing method of a flash memory device according to embodiments includes forming a plurality of gate patterns over a semiconductor substrate including a tunnel oxide layer, a floating gate, a dielectric layer, and a control gate. A spacer layer may be formed as a compound insulating layer structure over the side wall of the gate pattern. A source/drain area may be formed over the semiconductor substrate at both sides of the control gate. An insulating layer located at the outermost of the spacer layer may be removed. A contact hole may be formed between the gate patterns by forming and patterning the interlayer insulating layer. A contact plug may be formed in the contact hole.