Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a semiconductor substrate;
• a gate structure disposed on the semiconductor substrate;
• a first drift region disposed in the semiconductor substrate and located at a side of the gate structure;
• a first source/drain region disposed in the first drift region;
• a gate oxide layer disposed on the semiconductor substrate, wherein the gate oxide layer comprises:
• a first portion, wherein at least a part of the first portion is disposed between the gate structure and the semiconductor substrate in a vertical direction;
• and
• a second portion disposed between the first portion of the gate oxide layer and the first source/drain region in a horizontal direction, wherein the second portion of the gate oxide layer comprises a bottom extending downwards and a first depressed top surface located above the bottom in the vertical direction, and a part of the first drift region is located under the first portion of the gate oxide layer and the second portion of the gate oxide layer in the vertical direction;
• and
• a spacer structure disposed on a sidewall of the gate structure, wherein the spacer structure is disposed on the first portion of the gate oxide layer and the second portion of the gate oxide layer in the vertical direction, and the spacer structure directly contacts the first depressed top surface of the second portion of the gate oxide layer,
• wherein a bottom of the first portion of the gate oxide layer is higher than the bottom of the second portion of the gate oxide layer in the vertical direction.