Semiconductor device and method of fabricationg the same

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

• forming first gate patterns on a semiconductor substrate using an etch mask pattern;
• forming a trench in the semiconductor substrate between the first gate patterns;
• forming an insulating layer in the trench, such that the insulating layer fills the trench and cover a top of the etch mask pattern;
• planarizing the insulating layer to expose the top surface of the etch mask pattern;
• etching a portion of the planarized insulating layer to form a device isolation pattern in the trench;
• forming a second gate layer to fill the trench, such that second gate layer is on the device isolation pattern and on the top of the etch mask pattern;
• planarizing the second gate layer to expose the top surface of the etch mask pattern, such that a second gate pattern is formed;
• removing a portion of the second gate pattern;
• removing etch mask pattern, such that a top surface of the first gate pattern is exposed;
• and
• polishing simultaneously the first and second gate patterns to form a uniform flat surface.