Due to its coding nature, the many chemical and enzymatic manipulations that it can undergo, and its relative stability, DNA is being used as a scaffold and a building block outside the cellular context. The mode by which the DNA is connected to a solid surface is in the heart of technological advancements, such as DNA chips and biosensors. The desire is to connect the DNA to a given surface in a predesigned manner, tailored to any device specifications. In this work, DNA molecules were adsorbed specifically on gold surfaces. The specificity of the adsorption was controlled by a novel approach, in which the gold surface was first blocked with a hydrophobic layer (C-18-SH) to various extents, followed by the adsorption of thiolated DNA. The technique was applied both for short and for long strands of DNA. We show that the reactivity of the thiolated short DNA in a ligation reaction is enhanced by more than an order of magnitude by the presence of the alkylthiol layer. Due to the hydrophobic and insulating nature of the C-18-SH layer, this blocking method is advantageous for electronic measurements.