The growth behavior of GaAs/AlGaAs epilayers grown on U-shape patterned fusion GaAs(1 0 0) layer on InP substrate has been investigated. The wet etched side-plane of the U-shape pattern of the GaAs fusion layer was (2 1 1)A and (I I 1)B, for stripes aligned along [0(1) over bar 1] and [0 1 1] directions, respectively, whereas (1 1 1)A plane is preferred for both cases in normal GaAs substrates. The evolution of U-shape pattern sidewall from (2 1 1)A to (4 3 3)A for [0(1) over bar 1] direction and from (111)B to (411)B for CO 111 direction was revealed as the growth of GaAs/AlGaAs multi-layers proceeded. The abnormal sidewall facets were considered to be closely related with the fused layers and the enhancement of the lateral growth rate was a major factor to form high-quality epitaxial layers grown on the patterned GaAs fusion layer on InP substrate. These results will be eventually implemented for the fabrication of quantum structures such as quantum wires and dots formed on patterned fusion layers.