A semiconductor device includes a substrate including a lower substrate layer, a buried insulation layer on the lower substrate layer, and an upper substrate layer on the buried insulation layer, a first trench passing through the upper substrate layer, the buried insulation layer, and a portion of the lower substrate layer, a second trench passing through the upper substrate layer, the buried insulation layer, and a portion of the lower substrate layer and being spaced apart from the first trench, a field insulation layer in a portion of the first trench and in a portion of the second trench, and a first fin pattern defined by the first trench and the second trench. An upper surface of the field insulation layer is higher than an upper surface of the buried insulation layer.