A semiconductor structure and a method for fabricating the same. A semiconductor structure includes a semiconductor substrate; a channel region formed in the semiconductor substrate; a gate including a dielectric layer and a conductive layer and formed above the channel region; source and drain regions formed at opposing sides of the gate; first shallow trench isolations embedded into the semiconductor substrate and having a length direction parallel to the length direction of the gate; and second shallow trench isolations, each of which abuts the outer sidewall of the source or the drain region and abuts the first shallow trench isolations, in which the source and drain regions include first seed crystal layers abutting the second shallow trench isolations, and the top surfaces of the second shallow trench isolations are higher than or as high as the top surfaces of the source and drain regions.