A semiconductor laser device includes a substrate having a first surface and a second surface opposite to the first surface, an active region formed on the second surface of the substrate, a cladding layer formed on the active region, and an insulation region formed in the cladding layer to form on the second surface of the substrate a first laser region having a first size and a second laser region having a second size different from the first size. The first laser region is used for generating a first optical spectrum having a first laser mode channel space. The second laser region is used for generating a second optical spectrum having a second laser mode channel space. A combination of the first optical spectrum and the second optical spectrum forms a single mode laser. Without any gratings, the semiconductor laser device is easy to be fabricated and has a low fabrication cost.