A semiconductor device includes a device isolation layer defining first and second active regions, a buried contact connected to the second active region, and first and second bit line structures disposed on the first and second active regions. Each of the first and second bit line structures comprises a bit line contact part and a bit line pass part. The bit line contact part is electrically connected to the first active region. The bit line pass part is disposed on the device isolation layer. A height of a lowest part of the buried contact is smaller than a height of a lowest part of the bit line pass part. The height of the lowest part of the buried contact is greater than a height of a lowest part of the bit line contact part. A lower end of the bit line pass part is buried in the second active region.