Provided are a microfluidic device that performs a biochemical reaction using a small amount of a biochemical fluid and detects the result thereof, and a method of fabricating the same. The microfluidic device includes: a substrate which comprises a chamber that is formed as a concave groove and accommodates a fluid in the bottom surface of the substrate, and is formed of polymer; and a film welded on the bottom surface of the substrate to seal the chamber so that the chamber is not open at the bottom surface of the substrate, and formed of polymer. The method of fabricating a microfluidic device includes: preparing a substrate which comprises a chamber that is formed as a concave groove and accommodates a fluid in the bottom surface of the substrate, and is formed of polymer; and welding a film on a bottom surface of the substrate to seal the chamber so that the chamber is not opened at the bottom surface of the substrate, the film being formed of polymer.