An image sensor has a three-dimensional structure in which a sensor element array having a plurality of sensor elements consisting of CdTe, arranged in a two-dimensional matrix, is mounted to an IC substrate via a connection layer. The connection layer has a plurality of stud bumps and a plurality of thin film layers. The stud bumps are formed on an electrode of each IC and are provided in the connection layer in order to fetch a signal detected by each sensor element. The thin film layers are formed at the distal end of each stud bump, and are electrically connected with an electrode of each sensor element.