Some embodiments of the present disclosure provide a semiconductor structure, including a substrate having a top surface; a first doped region in proximity to the top surface; a non-doped region positioned in proximity to the top surface and adjacent to the first doped region, having a first width; a metal gate positioned over the non-doped region and over a portion of the first doped region, having a second width. The first width is smaller than the second width, and material constituting the non-doped region is different from material constituting the substrate.