A wiring substrate 20, comprising a glass substrate, which is provided with through holes 20c, each having a tapered part 20d that becomes large in opening area at the side of an input surface 20a, and conductive members 21, formed on the inner walls of through holes 20c, is used. A semiconductor device 5 is arranged by connecting bump electrodes 17, provided on an output surface 15b of a PD array 15 in correspondence with conductive members 21, to input portions 21a of conductive members 21 formed on input surface 20a of wiring substrate 20. A radiation detector is arranged by connecting a scintillator 10 via an optical adhesive agent 11 to a light-incident surface 15a of PD array 15 and connecting a signal processing element 30 via bump electrodes 31 to output surface 20b of wiring substrate 20. A semiconductor device, with which the semiconductor elements and the corresponding conductive paths of the wiring substrate are connected satisfactorily, and a radiation detector using this semiconductor device are thus provided.