Nitride semiconductor substrate and method for manufacturing same

A nitride semiconductor substrate comprising:

• a sapphire substrate;
• and
• a nitride semiconductor layer formed on the sapphire substrate and containing a group III element including Al and nitrogen as a main component,
• wherein a surface of the sapphire substrate where the nitride semiconductor layer is formed includes recesses having a maximum opening size of from 2 nm to 60 nm in an amount of from 1×109 pieces to 1×1011 pieces per cm2, in which a space is formed by each of the recesses and a surface of the nitride semiconductor layer immediately above each recess;
• of a surface of the nitride semiconductor layer on the sapphire substrate side, a height difference between the surface immediately above the each recess and a surface in contact with a flat surface is 10 nm or less;
• and a portion of the nitride semiconductor layer above the each recess has a crystalline structure produced by growth along a polar plane of the group III element.