To provide a grooving processing method capable of improving the measurement precision of a grooving method which is a simple evaluation.

In order to detect light emission characteristics of an epitaxial wafer 1 in which an epitaxial layer containing a light emitting layer 2 is formed on a substrate, grooving is applied for forming a trench 4 around a measurement part 3 of an arbitrary position of the epitaxial wafer 1. In this method, a cross section of the trench 4 is formed as an inverted trapezoid from the surface of the epitaxial wafer 1 toward the substrate side, so that a cross section of the measurement part 3 is formed into a trapezoid.