We present new evidence that two electron traps observed in polycrystalline zinc oxide can be associated with complex intrinsic defects. One deep level, E1, can be assigned to an oxygen vacancy. The second deep level, E2, could consist of a cluster‐type defect associated with oxygen vacancies. The two traps were characterized using deep‐level transient spectroscopy. The energies of these traps are 0.15 and 0.24 eV, the capture cross sections are 4×10−18and 1×10−17cm2, and the emission rates at 300 K are 2.0×106and 1.3×105Hz, respectively. The relative concentrations of these traps varied uniformly as a function of the cooling rate of the zinc oxide from a sintering temperature of 1300 °C. The concentration of E1 decreased, while the concentration of E2 increased, with decreasing cooling rate.