Semiconductor devices, in particular nitride semiconductor devices for use in the manufacture of laser diodes, prevent peeling-off of the electrode, and at the same time reduces the complexity of processes and a reduction in yield. A nitride semiconductor device according to the invention includes a P-type nitride semiconductor layer with a ridge on its surface, an SiO2 film covering at least the side face of the ridge, an adherence layer formed on a surface of the SiO2 film and composed mainly of silicon, and a P-type electrode formed on the upper surface of the ridge and on a surface of the adherence layer.