Optimum growth conditions were investigated to obtain high quality heteroepitaxial GaAs layers on InP substrates by liquid phase epitaxy (LPE). Addition of about 0.005wt% of Se to the Ga growth melt effectively suppressed dissolution of the InP substrates into the melt during the initial stage of the growth, resulting in a significantly improved surface morphology. The crystallinity and the surface morphology could be further improved by growing undoped GaAs layers on thin Se-doped buffer GaAs as well as using InP substrates patterned with grating structure. The transmission electron microscopy observation indicated that the misfit dislocations interact with each other at the grating region, resulting in a lower dislocation density in the upper GaAs layer. The (400) double crystal X-ray diffraction peaks of the undoped GaAs showed fullwidth- at-half-maximum of about 380 arcsec, which is comparable with the previously reported values using more sophisticated growth techniques.