Transistor, semiconductor device including a transistor and methods of manufacturing the same

A transistor, a semiconductor device including the transistor and methods of manufacturing the same are provided, the transistor including a threshold voltage adjusting layer contacting a channel layer. A source electrode and a drain electrode contacting may be formed opposing ends of the channel layer. A gate electrode separated from the channel layer may be formed. A gate insulating layer may be formed between the channel layer and the gate electrode.