An opto-semiconductor device. An opto-semiconductor element includes a semiconductor substrate, a multilayered semiconductor layer formed on a first surface of the semiconductor substrate and having a resonator, a first electrode with multiple conductive layers formed on the multilayered semiconductor layer, and a second electrode formed on a second surface of the semiconductor substrate. A support substrate has a first surface formed with a fixing portion having a conductive layer for fixing the first electrode connected thereto through a bonding material. Bonding material and conductive layers forming the first electrode react to form a reaction layer. The difference in thermal expansion coefficient between semiconductor substrate and support substrate is not more than .+-.50%. A second barrier metal layer not reactive with bonding material is formed inside the first electrode uppermost conductive layer, while uppermost layer reacts with the bonding material to form the reaction layer.