A method of fabricating a gallium nitride-based semiconductor electronic device is provided, the method preventing a reduction in adhesiveness between a gallium nitride-based semiconductor layer and a conductive substrate. A substrate 11 is prepared. The substrate 11 has a first surface 11a and a second surface 11b, the first surface 11a allowing a gallium nitride-based semiconductor to be deposited thereon. The substrate 11 includes a support 13 of a material different from the gallium nitride-based semiconductor. The support is exposed on the second surface 11b of the substrate 11. An array of grooves 15 is provided in the second surface 11b. A semiconductor region including at least one gallium nitride-based semiconductor layer is deposited on the first surface 11a of the substrate 11, and thereby an epitaxial substrate E is fabricated. A conductive substrate 33 is bonded to the epitaxial substrate E such that the semiconductor region 17 is provided between the first surface 11a of the substrate 11 and the conductive substrate E. Subsequently, the second surface 11b is irradiated with laser light for laser lift-off.