A semiconductor light emitting device including: a support substrate; a composite connection layer formed above the support substrate, the composite connection layer including a first connection layer and a second connection layer; a diffusion barrier layer formed above the composite connection layer; a semiconductor lamination structure formed above the diffusion barrier layer; and a reflective electrode layer formed between the diffusion barrier layer and the semiconductor lamination structure, wherein: at least one of the first and second connection layers is made of eutectic material; and the diffusion barrier layer has a lamination structure having TaN layers sandwiching at least one refractory metal layer made of one or more refractory metal materials of Ta, Ti, Mo, W and TiW or alloy thereof. It is possible to prevent defects such as stripping and cracks at bonding planes and improve reliability of a final semiconductor light emitting device.