We investigated the quantum well intermixing (QWI) of a compressively strained InGaAs/InGaAsP multiple quantum well (MQW) by using impurity free vacancy diffusion technique. The samples with InGaAs/$SiO_2$ capping layer showed a higher degree of intermixing compared to that of InP/$SiO_2$ capping layer after rapid thermal annealing (RTA). Band-gap shift difference as large as 123 meV (195 nm) was observed between samples capped with InGaAs/$SiO_2$ and with InP/$SiO_2$ layer at RTA temperature of $700^{circ}C$. Using the InGaAs/$SiO_2$ cap layer, the band-gap wavelength of MQW was changed by the intermixing from 1.55 $mu extrm{m}$ band to 1.3 $mu extrm{m}$ band with a wavelength shift of a 237 nm. The transform from MQW structure to homogenous alloy was observed above the RTA temperature of $700^{circ}C$.