Disclosed are a semiconductor device and a manufacturing method thereof. The semiconductor device can include a recess formed in an active area of a semiconductor substrate, an insulating layer formed in the recess, a source electrode and a drain electrode spaced apart from the source electrode on the insulating layer, a carbon nanotube layer formed between the source and drain electrodes, an oxide layer pattern covering at least the carbon nanotube layer, and a gate electrode formed on the oxide layer pattern.