PURPOSE: To obtain an optical integrated circuit which is provided with an optical joint part having a butt joint structure with high optical joint efficiency by applying a dry etching to a part of already piled-up first semiconductor layer to expose an end face and by growing a second semiconductor layer on a substrate in a manner that the second layer will be successively connected to the exposed end face.

CONSTITUTION: An optical enclosed layer 12 made of InGaAsP is piled up on an InP substrate 11 through a first growth, and further an active layer 13 having a quantum well structure is piled up on the layer 12. Then, an optical confinement layer 14 having the same composition as that of the layer 12 is piled up on the layer 13 and an InP clad layer 15 is piled up on the layer 14 thereafter. Such a formed layer structure body is subject to dry etching by an RIE method using an SiO2 mask and its right half is removed. Furthermore, following the dry etching, semiconductor layers 13'-15' corresponding to the layers 13-15 are successively piled up in the right half area where the semiconductor layer is removed, by a MOVPE method.