Provided is a III nitride semiconductor electronic device having a structure capable of reducing leakage current. A laminate 11 includes a substrate 13 and a III nitride semiconductor epitaxial film 15. The substrate 13 is made of a III nitride semiconductor having a carrier concentration of more than 1×1018 cm−3. The epitaxial structure 15 includes a III nitride semiconductor epitaxial film 17. A first face 13a of the substrate 13 is inclined at an angle θ of more than 5 degrees with respect to an axis Cx extending in a direction of the c-axis. A normal vector VN and a c-axis vector VC make the angle θ. The III nitride semiconductor epitaxial film 17 includes first, second and third regions 17a, 17b and 17c arranged in order in a direction of a normal to the first face 13a. A dislocation density of the third region 17c is smaller than that of the first region 17a. A dislocation density of the second region 17b is smaller than that of the substrate 13.