A gallium nitride crystal substrate has a diameter of 50-155 mm and a thickness of 300-800 μm and includes any of a flat portion and a notch portion in a part of an outer edge. The gallium nitride crystal substrate contains any of oxygen atoms, silicon atoms, and carriers at a concentration of 2×1017 to 4×1018 cm−3, and has an average dislocation density of 1000 to 5×107 cm−2 in any of a first flat region extending over a width from the flat portion to a position at a distance of 2 mm in a direction perpendicular to a straight line indicating the flat portion in a main surface and a first notch region extending over a width from the notch portion to a position at a distance of 2 mm in a direction perpendicular to a curve indicating the notch portion in the main surface.