An array of monolithic wavelength division multiplexed (WDM) vertical cavity surface emitting lasers (VCSELs) is provided with quantum well intermixing. Each VCSEL includes a bottom distributed Bragg reflector (DBR), an upper distributed Bragg reflector, and a laser cavity therebetween. The laser cavity includes a multiple quantum well (MQW) layer sandwiched between a lower separate confinement heterostructure (SCH) and an upper SCH layer. Each MQW region experiences a different amount of quantum well intermixing and concomitantly a different lasing wavelength shift.