Manufacturing method of semiconductor device with increased drain breakdown voltage

A method of manufacturing a semiconductor device, comprising:

• forming a gate insulating film and a gate electrode that has a first end portion and a second end portion on a semiconductor substrate of a first conductivity type;
• forming a first drain region by implanting at a first dosage a first impurity of a second conductivity type corresponding to an opposite conductivity type with respect to the first conductivity type at a vicinity of the first end portion of the gate electrode in the first-side region of the semiconductor substrate in respect to the gate electrode;
• forming a second drain region to be overlapped with the first drain region by implanting a second impurity of the second conductivity type at a second dosage that is substantially equal to the first dosage in the first-side region of the semiconductor substrate, and implanting the second drain region with an implantation energy that is greater than the implantation energy used for implanting the first impurity;
• and
• forming a drain contact region within the second drain region by implanting a third impurity of the second conductivity type at a third dosage that is greater than the second dosage;
• wherein the first drain region has a third end portion, a fourth end portion, a fifth end portion and a sixth end portion,
• the third end portion and the fourth end portion are opposite each other,
• the fifth end portion and the sixth end portion are opposite each other,
• the third end portion is nearer than the fourth end portion from the gate electrode,
• the second drain region has a seventh end portion, an eighth end portion, a ninth end portion and a tenth end portion,
• the seventh end portion and the eighth end portion are opposite each other,
• the ninth end portion and the tenth end portion are opposite each other,
• the seventh end portion is located between the third end portion and fourth end portion,
• the eighth end portion is more distant than the fourth end portion from the gate electrode, and
• the ninth end portion and the tenth end portion are more distant than the fifth end portion and sixth end portion from the drain contact region respectively.