Studies of space‐charge‐limited currents as a function of sample thicknessLwere made for CdS and naphthalene monocrystals. In naphthalene, where the current‐voltage curves show the behavior expected for a discrete trap energy above the Fermi level, we findVTFLessentially independent ofL. We attribute this result to the presence of few filamentary regions oriented along thecaxis and differing only slightly from the bulk in distribution of defects. For CdS we findVTFL∝L, consistent with a constant upper field limit of 1.6 × 104V/cm on a one‐carrier injection current. In neither material can the volume concentration of traps be determined from the voltage at which the current rises sharply.