In order to solve the contradiction between large optical cavity (LOC) and low threshold current, a new semiconductor laser which has three quantum wells with higher barrier and asymmetric broad waveguide structure is designed. The laser can sustain low threshold current with large optical cavity. GaAs/AlGaAs three quantum wells and 3.6 μm super large optical cavity waveguide are grown by metal organic chemical vapor deposition (MOCVD). The 980 nm semiconductor laser is fabricated. As a result, the threshold current of 4 mm LOC semiconductor laser is 1105.5 mA and the vertical divergence angle is 15.6°. An output power of 15.9 W is reached with injection current of 25 A. The results show that the designed structure is effective for light field expanding, which can realize large optical cavity and guarantee low threshold current.