An optical semiconductor element having a mesa portion includes a substrate and semiconductor layers on the substrate. The optical semiconductor element further includes a first contact electrode, a second contact electrode on the semiconductor layer, first and second lead-out wires connected to the first and second contact electrodes, respectively, and an insulating film covering at least an upper surface of the semiconductor layer and the second contact electrode. The second lead-out wire is connected to the second contact electrode in an opening of the insulating film. An outer peripheral end of the second contact electrode in at least a portion where the second contact electrode and the second lead-out wire are connected is above and outside an outer peripheral end of a connection portion with the semiconductor layer, and an inner peripheral end is above and inside an inner peripheral end of the connection portion with the semiconductor layer.