Disclosed are a nitride based semiconductor device, including a high-quality GaN layer formed on a silicon substrate, and a process for preparing the same. A nitride based semiconductor device in accordance with the present invention comprises a plurality of nanorods aligned and formed on the silicone substrate in the vertical direction; an amorphous matrix layer filling spaces between nanorods so as to protrude some upper portion of the nanorods; and a GaN layer formed on the matrix layer.