Nominally pure and gallium doped single crystals of potassium titanyl phosphate (KTiOPO 4 ) have been studied by Electron Paramagnetic Resonance at low temperatures before and after irradiation. Irradiation with 20 MeV electrons performed at room temperature and liquid nitrogen temperature caused an appearance of electrons and holes. Gallium impurities act as hole traps in KTiOPO 4 creating Ga 4þ centers. Two different Ga 4þ centers were observed, Ga1 and Ga2. The Ga1 centers are dominant in Ga-doped samples. For the Ga1 center, a superhyperfine structure with one nucleus with nuclear spin 1 = 2 was registered and attributed to the interaction of gallium electrons with a phosphorus nucleus or proton in its surrounding. In both Ga1 and Ga2 centers, Ga 4þ ions substitute for Ti 4þ ions, but with a preference to one of two electrically distinct crystallographic positions (site selective substitution). The Ga doping eliminates one of the shortcomings of KTP crystalsionic conductivity of bulk crystals. However, this does not improve significantly the resistance of the crystals to electron and c-radiation. V C 2014 AIP Publishing LLC.