A GaN semiconductor light-emitting element is provided. The GaN semiconductor light-emitting element includes an island-type seed region composed of a GaN-based compound semiconductor disposed on a substrate; an underlying layer having a three-dimensional shape composed of a GaN-based compound semiconductor, disposed on at least the seed region; a first GaN-based compound semiconductor layer of a first conductivity type, an active layer composed of a GaN-based compound semiconductor, and a second GaN-based compound semiconductor layer of a second conductivity type disposed in that order on the underlying layer; a first electrode electrically connected to the first GaN-based compound semiconductor layer; and a second electrode disposed on the second GaN-based compound semiconductor layer. The top face of the seed region is the A plane, and at least one side face of the underlying layer is the S plane.