The present invention provides a semiconductor structure, the semiconductor structure includes a substrate, at least one active area is defined on the substrate, a buried word line is disposed in the substrate, a source/drain region disposed beside the buried word line, a diffusion barrier region, disposed at the top of the source/drain region, the diffusion barrier region comprises a plurality of doping atoms selected from the group consisting of carbon atoms, nitrogen atoms, germanium atoms, oxygen atoms, helium atoms and xenon atoms, a dielectric layer disposed on the substrate, and a contact structure disposed in the dielectric layer, and electrically connected to the source/drain region.