The present invention provides a semiconductor structure comprising a substrate; a gate stack on the substrate; a spacer on the sidewalls of the gate stack; a source/drain junction extension formed in the substrate on both sides of the gate stack by epitaxial growth; and a source/drain region in the substrate on both sides of the source/drain junction extension. Accordingly, the present invention also provides methods for manufacturing the semiconductor structure. The present invention can provide a source/drain junction extension with a high doping concentration and a low junction depth, thereby effectively improving the performance of the semiconductor structure.