A semiconductor device includes first and second fins on first and second regions of a substrate, a first trench overlapping a vertical end portion of the first fin and including first upper and lower portions, the first upper and lower portions separated by an upper surface of the first fin, a second trench overlapping a vertical end portion of the second fin and including second upper and lower portions separated by an upper surface of the second fin, a first dummy gate electrode including first metal oxide and filling layers, the first metal oxide layer filling the first lower portion of the first trench and is along a sidewall of the first upper portion of the first trench, and a second dummy gate electrode filling the second trench and including second metal oxide and filling layers, the second metal oxide layer extending along sidewalls of the second trench.