Metal contacts are formed within a string overhead area using a double patterning technology (DPT) process thereby allowing for the reduction of a string overhead area and a concomitant reduction in the chip size of a semiconductor device. A first mask pattern is formed by etching a first mask layer, the first mask pattern including a first opening formed in a cell region and a first hole formed in a peripheral region. A first sacrificial pattern is formed on the first mask pattern and the exposed first insulating layer of the cell region using a double patterning technology process. Contact holes are formed by exposing the target layer by etching the first insulating layer using the first mask pattern and the first sacrificial pattern as an etch mask. Metal contacts are then formed in the contact holes.