A method of determining defects in photomasks according to the present invention is designed to increase the yield of the manufacture of photomasks and to decrease the cost of inspecting the photomasks. In the method, circuit data 1 representing a circuit to be formed on a semiconductor substrate by photolithography is prepared, and layout data 2 is prepared from the circuit data 1. The layout data is converted to compensated layout data by performing RET. Further, mask-manufacturing data is developed from the compensated layout data. To form patterns on a semiconductor substrate by photolithography, attribute information is imparted to the mask-manufacturing data. The attribute information represents whether the patterns are adaptive to electrically active regions or electrically non-active region. In the mask-inspecting process 6, a criterion for determining whether the patterns formed on the photomasks have defects is changed in accordance with the attribute information.