A radiation detector of this invention includes a Cl-doped CdTe or Cl-doped CdZnTe polycrystalline semiconductor film in which defect levels in crystal grains are protected. This is obtained by grinding CdTe or CdZnTe crystal doped with Cl, and preparing the polycrystalline semiconductor film again by using its powder as the source. The defect levels of crystal grain boundaries in the polycrystalline semiconductor film are also protected by further doping the polycrystalline semiconductor film prepared again with Cl. These features enable manufacture of the radiation detector which has excellent sensitivity and response to radiation.