A transistor for emitting laser with a fixed frequency includes a first region, a second region, at least one quantum well, and a third region. The at least one quantum well is installed in the second region, and the second region is coupled between the first region and the third region. When one of the first region, the second region, and the third region receives two signals, or two of the first region, the second region, and the third region receive the two signals respectively, the at least one quantum well emits the laser with the fixed frequency.