Provided is an optical semiconductor element in which an unbonded portion between an optical semiconductor chip and a submount is made small, heat dissipation efficiency becomes high, and service life can be made long. The optical semiconductor element can include: a submount; a submount electrode provided on a mounting surface of the submount and having a rectangular shape as a whole; and a semiconductor chip including an element substrate, a semiconductor structure layer formed on the element substrate, and a chip electrode bonded to the submount electrode via a bonding layer. The chip electrode has a shape with chipped corners corresponding to four corners of the submount electrode, which has an exposed surface that is a portion exposed from the chip electrode at the four corners and bonded to the chip electrode to coincide with each other. The bonding layer extends to all the four corners of the exposed surface.