Transistor and manufacturing method thereof

A method for manufacturing a transistor, comprising:

• providing a well region disposed in a substrate;
• forming a gate structure disposed above the well region;
• forming a gate oxide layer disposed between the gate structure and the well region, wherein a first portion of the gate oxide layer is thicker than a second portion of the gate oxide layer;
• forming a first doped region and a second doped region arranged in the well region, wherein the first doped region and the second doped region are located at two opposite sides of the gate structure in a horizontal direction, wherein the distance between the first doped region and the first portion of the gate oxide layer is greater than the distance between the second doped region and the second portion of the gate oxide layer along the horizontal direction, and a conductivity type of the first doped region is the same as a conductivity type of the second doped region;
• and
• forming a salicide block located on the substrate and at one side of the gate structure, wherein the salicide block is located between the first portion of the gate oxide layer and the first doped region.