A semiconductor device is manufactured by, inter alia: forming second gate lines, arranged at wider intervals than each of first gate lines and first gate lines, over a semiconductor substrate; forming a multi-layered insulating layer over the entire surface of the semiconductor substrate including the first and the second gate lines; etching the multi-layered insulating layer so that a part of the multi-layered insulating layer remains between the first gate lines and the first and the second gate lines; forming mask patterns formed on the respective remaining multi-layered insulating layers and each formed to cover the multi-layered insulating layer between the second gate lines; and etching the multi-layered insulating layers remaining between the first gate lines and between the first and the second gate lines and not covered by the mask patterns so that the first and the second gate lines are exposed.