A nitride semiconductor crystal growth method for growing a crystal of a nitride semiconductor on a principal nitride plane of a base at least one principal plane of which is a nonpolar nitride, the nitride semiconductor crystal growth method comprising: a heating step including a period t A during which the base is heated above about 450 °C in an atmosphere made up of a heating step main flow containing an inactive gas; a first growth step of epitaxially growing a first nitride semiconductor layer on the principal nitride plane of the base in an atmosphere made up of a first growth step main flow containing an inactive gas and without intentional supply of a silicon, Si, source material; and a second growth step of epitaxially growing a second nitride semiconductor layer on the first nitride semiconductor layer while supplying an n-type dopant source material in an atmosphere made up of a second growth step main flow containing an inactive gas; wherein the heating step, first growth step, and second growth step main flows comprise as a nitrogen source material at least one type of gas selected from ammonia, NH 3, gas, a hydrazine compound, an amine compound, and an azide compound, wherein the first and second growth steps main flows include at least a respective first main flow and a respective second main flow; the respective first main flow mainly supplies the nitrogen source material constituting the nitride semiconductor layers; and the respective second main flow supplies source materials for elements other than nitrogen constituting the nitride semiconductor layers, wherein the inactive gas is at least one type of gas selected from the group consisting of nitrogen, N 2, helium, He, Argon, Ar, Xenon, Xe, Krypton, Kr, a hydrazine compound, an amine compound, and an azide compound, wherein at least one of the heating step, first growth step, and second growth step has a period during which the atmosphere contains ammonia, NH 3, gas, during the period t A of the heating above 450 °C and in the first growth step, a flow ratio of the inactive gas component to all constituent gases of the main flow is between 0.5 and 1.0 both inclusive and, the heating pressure P A of the period t A in the heating step is 35 kPa or more and 120 kPa or less. a heating step including a period t A during which the base is heated above about 450 °C in an atmosphere made up of a heating step main flow containing an inactive gas; a first growth step of epitaxially growing a first nitride semiconductor layer on the principal nitride plane of the base in an atmosphere made up of a first growth step main flow containing an inactive gas and without intentional supply of a silicon, Si, source material; and a second growth step of epitaxially growing a second nitride semiconductor layer on the first nitride semiconductor layer while supplying an n-type dopant source material in an atmosphere made up of a second growth step main flow containing an inactive gas; wherein the heating step, first growth step, and second growth step main flows comprise as a nitrogen source material at least one type of gas selected from ammonia, NH 3, gas, a hydrazine compound, an amine compound, and an azide compound, wherein the first and second growth steps main flows include at least a respective first main flow and a respective second main flow; the respective first main flow mainly supplies the nitrogen source material constituting the nitride semiconductor layers; and the respective second main flow supplies source materials for elements other than nitrogen constituting the nitride semiconductor layers, wherein the inactive gas is at least one type of gas selected from the group consisting of nitrogen, N 2, helium, He, Argon, Ar, Xenon, Xe, Krypton, Kr, a hydrazine compound, an amine compound, and an azide compound, wherein at least one of the heating step, first growth step, and second growth step has a period during which the atmosphere contains ammonia, NH 3, gas, during the period t A of the heating above 450 °C and in the first growth step, a flow ratio of the inactive gas component to all constituent gases of the main flow is between 0.5 and 1.0 both inclusive and, the heating pressure P A of the period t A in the heating step is 35 kPa or more and 120 kPa or less.