Method of manufacturing nitride semiconductor substrates having a base substrate with parallel trenches

A method for manufacturing a nitride semiconductor substrate, comprising:

• forming a plurality of first trenches on a lower surface of a base substrate parallel to each other in a first direction;
• and
• forming a nitride semiconductor film on a top surface of the base substrate opposite to the first trench formation surface,
• wherein widths of the first trenches change towards a peripheral portion of the base substrate in a predetermined tendency.

A method for manufacturing a nitride semiconductor substrate, comprising:

• forming a plurality of first trenches on a lower surface of a base substrate parallel to each other in a first direction;
• and
• forming a nitride semiconductor film on a top surface of the base substrate opposite to the first trench formation surface,
• wherein depths of the first trenches change towards a peripheral portion of the base substrate in a predetermined tendency.