We show the formation of ultraslow bright and dark optical solitons in a cascade-type three-level system of GaAs/AlGaAs multiple quantum wells (MQWs) structure based on the biexciton coherence in the transient optical response, and study analytically and numerically with Maxwell–Schrödinger equations. The calculated velocity of bright and dark optical solitons are V g =2.7×10 4 ms −1 and V g =8.91×10 4 ms −1 , respectively. Such investigation of ultraslow optical solitons in MQWs may provide practical applications such as high-fidelity optical delay lines and optical buffers in semiconductor quantum wells structure, because of its flexible design.