A film forming apparatus includes a reaction chamber, a pedestal disposed inside the reaction chamber and configured to support a substrate, and a gas shower head over the pedestal. The gas shower head includes a plurality of first holes and a plurality of second hole disposed between a circumference of the gas shower head and the first holes. The first holes are arranged to form a first pattern and configured to form a first portion of a material film on the substrate. The second holes are arranged to form a second pattern and configured to form a second portion of the material film on the substrate. A hole density of the second pattern is greater than a hole density of the first pattern.