Integrated circuit device

An integrated circuit device comprising a semiconductor substrate and a first transistor and a second transistor constructed in the semiconductor substrate, the first transistor having a first operating voltage, the second transistor having a second operating voltage, the first operating voltage is higher than the second operating voltage,

• wherein the first transistor comprises:
• a first drain structure formed in the semiconductor substrate;
• a first source structure formed in the semiconductor substrate, and comprising a high voltage first-polarity well region, a first-polarity body region, a heavily doped first-polarity region, a second-polarity grade region and a heavily doped second-polarity region, wherein the heavily doped second-polarity region is surrounded by the second-polarity grade region, and the second-polarity grade region is surrounded by the first-polarity body region;
• an isolation structure formed in the semiconductor substrate, and arranged between the first drain structure and the first source structure;
• and
• a first gate structure arranged between the first source structure and the first drain structure, and partially disposed over the isolation structure,
• wherein the second transistor comprises:
• a second drain structure formed in the semiconductor substrate;
• a second source structure formed in the semiconductor substrate;
• a second gate structure formed in the semiconductor substrate, and arranged between the second source structure and the second drain structure;
• and
• a second-polarity drift region formed in the semiconductor substrate for at least surrounding the second drain structure, wherein the second-polarity drift region and the second-polarity grade region have the same dopant concentration.