Electron spin resonance (ESR), electron‐nuclear double resonance (ENDOR), and optical absorption have been used to investigate radiation effects in synthetic crystals of berlinite (AlPO4). Crystals from seeded and unseeded growth were included in the study and impurities in both types of samples were determined by emission spectrographic techniques. The presence of significant concentrations of Fe3+ions was verified by ESR measurements. When the berlinite samples were irradiated at 300 K with 1.7‐MeV electrons, six distinct hole‐like centers were created. Thermal anneal studies revealed that four of these centers decay near 425 K and the other two decay at 550 K. All six centers exhibited a hyperfine interaction with a 100% abundantI=1/2 nucleus. The irradiation induced a light orange coloration in the crystals and optical absorption spectra revealed a band at 520 nm along with additional absorption in the ultraviolet region. When the samples were irradiated at 77 K, two additional defects were produced which are not stable at room temperature. One of these latter centers is identified as atomic hydrogen.