We have developed a planar device using In-Ga-Zn-O (IGZO) semiconductor for synapse element in neural network. First, we formed the planar device on a glass substrate. Next, we formed it on an LSI wafer. Both devices shows proper uniformities of film thicknesses and sufficient degradations of electric characteristics, which can be utilized for modified Hebbian learning proposed by us. These results suggest a great possibility for neural networks using planar devices using IGZO semiconductor for synapse elements.