Provided are a method of manufacturing a transparent N-doped p-type ZnO semiconductor layer using a surface chemical reaction between precursors containing elements constituting thin layers, and a thin film transistor (TFT) including the p-type ZnO semiconductor layer. The method includes the steps of: preparing a substrate and loading the substrate into a chamber; injecting a Zn precursor and an oxygen precursor into the chamber, and causing a surface chemical reaction between the Zn precursor and the oxygen precursor using an atomic layer deposition (ALD) technique to form a ZnO thin layer on the substrate; and injecting a Zn precursor and an nitrogen precursor into the chamber, and causing a surface chemical reaction between the Zn precursor and the nitrogen precursor to form a doping layer on the ZnO thin layer.