A method for fabricating a semiconductor device including: cleaning an apparatus used to grow a layer including Ga; performing a first step of forming a first layer on a substrate made of silicon by using the apparatus, the first layer including a nitride semiconductor that does not include Ga as a composition element and has a Ga impurity concentration of 2×1018 atoms/cm3 or less; and performing a second step of forming a second layer on the first layer by using the apparatus after the first step is repeatedly carried out multiple times, the second layer including a nitride semiconductor including Ga.