A semiconductor device includes a substrate including a first trench, a first fin pattern on the substrate that is defined by the first trench, a gate electrode on the substrate, and a field insulating layer on the substrate. The first fin pattern includes an upper part on a lower part. The first fin pattern includes a first sidewall and a second sidewall opposite each other. The first sidewall is concave along the lower part of the first fin pattern. The second sidewall is tilted along the lower part of the first fin pattern. The field insulating layer surrounds the lower part of the first fin pattern. The gate electrode surrounds the upper part of the first fin pattern.