Cross-sectional scanning tunneling microscopy (STM) and scanning tunneling spectroscopy are used to study strain-compensated InGaAsP/InAsP superlattices grown by metalorganic vapor phase epitaxy, with or without an InP layer inserted in the InAsP barrier. A difference of contrast in the STM images is observed between the InAsP barrier grown over an InP layer compared with the InAsP grown over the InGaAsP well. The first approximate to 4 nm of the InAsP barrier layers grown over the wells are found to be compositionally intermixed, containing significant enrichment of both arsenic and gallium atoms. This intermixing is believed to be due to some carryover or surface segregation of these species when the growth is switched from well to barrier.