We present a cross-sectional scanning tunneling microscopy (XSTM) study of the spontaneous ordering ofGa0.48In0.52PandGa0.52In0.48Pgrown on (001) GaAs substrates by molecular beam epitaxy (MBE) and organometallic vapor phase epitaxy (OMVPE), respectively. The (111)-type alloy ordering could be seen clearly in the OMVPE-grown alloy region. On the other hand, the MBE-grown region shows a very small degree of ordering as revealed by the STM. Most of the ordered region shows(InP)1(GaP)1-type ordering: alternating InP- and GaP-like(1¯11)planes. In addition to this type of ordering, we also observe another type of ordering consisting of two InP-like(1¯11)planes and one GaP-like(1¯11)plane that we call(InP)2(GaP)1-type ordering. ©1998 American Institute of Physics.