Method for fabricating a semiconductor device including a gate structure with an inclined side wall

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

• forming an active pattern extending in a first direction on a substrate,
• forming a plurality of dummy gate electrodes spaced apart from each other and extending in a second direction intersecting the first direction, on the active pattern;
• forming an interlayer insulating film that covers side walls of the respective dummy gate electrodes;
• forming a first gate structure and a second gate structure, each extending in the second direction, in place of the plurality of dummy gate electrodes, after forming the interlayer insulating film;
• etching the interlayer insulating film and the active pattern between the first gate structure and the second gate structure to form a separation trench;
• and
• forming a device isolation film which fills the separation trench,
• wherein a side wall of the first gate structure facing the device isolation film includes a first inclined surface having an acute angle toward the first gate structure with respect to an upper surface of the active pattern such that a width of a portion of the first gate structure distal to the substrate is less than a width of a portion of the first gate structure proximate to the substrate, after forming the separation trench.