Abstract: A semiconductor device having superior light output efficiency is disclosed. A p-Si diffusion layer is formed on a Si substrate and an n-Si diffusion layer is formed in the p-Si diffusion layer. An n-GaAs layer constituting an active region for emitting light is grown on the p-Si diffusion layer and the n-Si diffusion layer of the Si substrate and a p-GaAs layer constituting an active region for emitting light is grown on the n-GaAs layer. An upper electrode is disposed on an upper surface of the p-GaAs layer above the p-Si diffusion layer. Current is injected from the upper electrode through a region of the pn junction between the n-GaAs layer and the p-GaAs layer other than that directly below the upper electrode, and light is emitted from this region. The emitted light passes through the p-GaAs layer to outside the device without passing through and being attenuated by the upper electrode.