A semiconductor laser using an external resonator. A laser diode chip emits a laser beam in a horizontal direction parallel to the bottom plane of a package, and the travel path of the laser beam is changed into a vertical direction by a reflective mirror next to a laser beam-emitting surface of the laser diode chip. As a result, the beam arrangement of the external cavity is available on a plane parallel to the bottom plane of the package through a lens installed on the vertical travel path of the laser beam. Consequently, the beam is easily arranged. Furthermore, an additional reflective mirror is installed above the lens which changes the vertical travel path into a horizontal travel path, which allows the beam traveling parallel to the bottom plane to be easily arranged through the lens. The production of the package can also be enabled in the configuration where various optical tools are arranged on the bottom of the package. Therefore, the semiconductor laser using an external cavity and having various characteristics can be easily manufactured.