The present invention provides a semiconductor structure, which comprises: a substrate, a semiconductor base, a semiconductor auxiliary base layer, a cavity, a gate stack, a sidewall spacer, and a source/drain region, wherein the gate stack is located on the semiconductor base; the sidewall spacer is located on the sidewalls of the gate stack; the source/drain region is embedded in the semiconductor base and is located on both sides of the gate stack; the cavity is embedded in the substrate; the semiconductor base is suspended above the cavity, the thickness of the middle portion of the semiconductor base is greater than the thickness of the two end portions of the semiconductor base in the direction of the length of the gate, and the two end portions of the semiconductor base are connected to the substrate in the direction of the width of the gate; and the semiconductor auxiliary base layer is located on the sidewall of the semiconductor base and has an opposite doping type to that of the source/drain region, and the doping concentration of the semiconductor auxiliary base layer is higher than that of the semiconductor base. Correspondingly, the present invention also provides a method for manufacturing a semiconductor structure. According to the present invention, the short channel effect can be suppressed, and the device performance can be improved, thereby reducing the cost and simplifying the process.