Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device, comprising:

• providing a semiconductor substrate, wherein the semiconductor substrate comprises a first portion located within a low voltage device region and a second portion located within a middle voltage device region;
• forming a first gate structure and a second gate structure above the first portion and the second portion, respectively;
• and
• performing an implantation process for forming a first source/drain doped region in the first portion and forming a second source/drain doped region in the second portion concurrently, wherein a first oxide layer is located above the first portion and a second oxide layer is located above the second portion during the implantation process, the first source/drain doped region is formed under the first oxide layer, the second source/drain doped region is formed under the second oxide layer, and a thickness of the second oxide layer is greater than or substantially equal to a thickness of the first oxide layer.