A semiconductor light emitting device comprising: a transparent substrate; an electron injection layer of N-type GaN-based semiconductor; an active layer on the electron injection layer; a hole injection layer of P-type GaN-based semiconductor on the active layer; a first electrode structure on the hole injection layer; a second electrode structure on the electron injection layer; and a circuit substrate flip-chip bonded with the electrode structures, wherein the first electrode structure comprises a contact metal structure which is mesh- or island-shaped on the hole injection layer to expose a surface portion of the hole injection layer, and a reflective layer which covers the contact metal structure and the exposed surface portion of the hole injection layer, at least an upper portion of the reflective layer being made of silver (Ag) or aluminum (Al), an area ratio of the contact metal structure to the first electrode structure satisfies a following inequality: 0.4.ltoreq.A.sub.pd/A.sub.total<1.