A semiconductor integrated circuit device may include: a substrate that includes a high-voltage device region and a low-voltage device region defined on the substrate; a first buried impurity layer formed in at least a portion of the high-voltage device region and coupled to a first voltage; a second buried impurity layer formed in at least a portion of the low-voltage device region and coupled to a second voltage less than the first voltage; and a well formed on the second buried impurity layer in the low-voltage device region and coupled to a third voltage less than the second voltage.