Semiconductor device having MOS varactor and methods for fabricating the same

A method of fabricating a semiconductor device, the method comprising:

• forming a lower insulating layer on a semiconductor substrate;
• forming a lightly doped semiconductor layer on the lower insulating layer;
• forming an active semiconductor plate by patterning the lightly doped semiconductor layer within a first region of the lower insulating layer;
• sequentially forming a dielectric layer and a metal layer on the semiconductor substrate having the active semiconductor plate;
• forming a metal gate electrode on the active semiconductor plate by sequentially patterning the dielectric layer and the metal layer within the first region of the lower insulating layer;
• forming a semiconductor resistor by patterning the lightly doped semiconductor layer within a second region of the lower insulating layer at the same time the lightly doped semiconductor layer within the first region of the lower insulating layer are pattern;
• forming a metal resistor on the semiconductor resistor by sequentially patterning the metal layer and the dielectric layer within the second region of the lower insulating layer at the same time sequentially patterning the metal layer and the dielectric layer within the first region of the lower insulating layer;
• and forming highly doped regions within the active semiconductor plate by implanting impurity ions into the active semiconductor plate, using the metal gate electrode as an ion implantation mask.