A newly developed method [J. Appl. Phys. 66, 3178 (1989)] in nuclear magnetic resonance (NMR) spin‐echo measurements, which allows us a precise determination of the quadrupolar interaction magnitude in crystals, has been applied to a series of undoped, liquid‐encapsulated Czochralski GaAs crystals. By varying the carbon concentration from 6×1014 to 1.4×1016 cm−3, it was verified that the quadrupolar interaction magnitude is proportional to the density of charged point defects in the crystal. The NMR method provides a feasible tool to detect ionized point defects of the order of as low as 1014 cm−3.