Methods of forming a semiconductor device and semiconductor device formed by the methods are provided. The methods of forming a semiconductor device may include providing a first substrate and a first bonding layer that is provided on the first substrate, forming a sacrificial pattern and an active pattern on a second substrate, forming a second bonding layer on the active pattern, bonding the second bonding layer onto the first bonding layer, removing the second substrate, and removing the sacrificial pattern to expose the active pattern. Forming the sacrificial pattern and the active pattern on the second substrate may include forming a preliminary sacrificial pattern and the active pattern on the second substrate and oxidizing the preliminary sacrificial pattern. The preliminary sacrificial pattern and the active pattern may be sequentially stacked on the second substrate.