A semiconductor device includes a first multi-channel active pattern defined by a field insulating layer and extending along a first direction, the first multi-channel active pattern including a first portion having a top surface protruding further in an upward direction than a top surface of the field insulating layer and a second portion on both sides of the first portion, the second portion having sidewalls with a continuous profile and a top surface protruding further in the upward direction than the top surface of the field insulating layer and protruding in the upward direction less than the top surface of the first portion, a gate electrode on the first portion of the first multi-channel active pattern and extending along a second direction different from the first direction, and a first source/drain region on the second portion of the first multi-channel active pattern and contacting the field insulating layer.