Measurements of space‐charge‐limited currents (SCLC) and thermally stimulated currents (TSC) were done in naphthalene single crystals grown from the melt and also from solution. Crystals grown from the melt were irradiated with x rays to a dose that ranged between 8×104and 6×106R. These crystals were also doped with beta naphthol with concentrations that varied from 10−4to 10−2in mole fraction. Melted crystals showed a trap level at 0.71 eV using SCLC and 0.79 eV using TSC, whereas solution crystals showed 0.43 eV using SCLC and 0.78 eV using TSC. Irradiated samples showed a trap level at 0.50 eV. In the case of doped samples the impurities originate a trap level at a depth of 0.53 eV that was possible to predict theoretically. Results showed that care must be exercised to obtain a valid comparison between the SCLC and TSC measurements and also that trapping of charge carriers is greatly influenced by the conditions under which the crystals were grown.