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 .