A method of manufacturing a thin film integrated circuit device according to the present invention includes steps of forming a peel-off layer over a thermally oxidized silicon substrate, forming a plurality of thin film integrated circuit devices over the peel-off layer with a base film interposed therebetween, forming a groove between the plurality of thin film integrated circuit devices, and separating the plurality of thin film integrated circuit devices by introducing one of a gas and a liquid including halogen fluoride into the groove to remove the peel-off layer.