Transmission electron diffraction (TED) and reflection high-energy electron diffraction (RHEED) have been used to investigate GaInP molecular beam epitaxial layers grown at temperatures in the range 445-510 degreesC. TED results reveal the presence of diffracted intensity at 1/2(-1 1 1) and 1/2(1 -1 1) positions, indicating the occurrence of CuPt-B ordering. As the growth temperature decreases, the superlattice spots move toward 1/2{-1 + delta, 1 - delta, 0} positions, where the value of delta is 0.15, It is further shown that for the layers grown at temperatures in the range 445-490 degreesC, weak diffracted intensity is observed at 1/2(1 1 -1) and 1/2(1 1 1) positions, indicating the formation of CuPt-A ordering. Based on the TED and RHEED results, explanations are given to describe the formation of CuPt-A and CuPt-B type ordering. Photoluminescence results show that the samples grown at temperatures in the range 470-510 degreesC undergo a bandgap reduction. This is attributed to the presence of ordered structures and composition modulation.