An object of the present invention is to provide a Group III nitride semiconductor stacked structure with a low dislocation density obtained by stacking only a semiconductor layer on a flat substrate by the use of a normal epitaxial growth method without processing the substrate or a deposit layer on the substrate, wherein the dislocation density is 1×107 cm−2 or less.The inventive Group III nitride semiconductor stacked structure comprises a substrate having a surface roughness (Ra) of 1 nm or less and a Group III nitride semiconductor layer directly stacked on the substrate, wherein the Group III nitride semiconductor layer comprises a plurality of layers put into contact with each other, the plurality of layers comprise a high-concentration impurity atom layer and a low-concentration impurity atom layer, and the high-concentration impurity atom layer is present on the substrate side.