The dielectric breakdown characteristics of thin gate oxide prepared by trans 1,2-dichloroethylene (t-DCE:C2H2Cl2) added oxidation as a Substitution for 1,1,l-trichloroethane (1,1,1-TCA:CH3CCl3) have been investigated. The t-DCE was shown to have lower ozone depletion potential (ODP = 0.0001) than the 1,1,1-TCA (ODP = 0.1) and allows easy replacement of the 1,1,1-TCA. The interface characteristics were superior or comparable to the conventional pyrogenic oxidation. The dielectric breakdown reliability was improved by addition of t-DCE. The optimum t-DCE concentration depends on preoxidation cleaning condition. In the case of the SCl(NH4OH:H2O2:H2O) and subsequent DHF (HF:H2O) preoxidation cleaning, the optimum t-DCE concentration is 5 weight percent (w/o). In the case of the SCl preoxidation cleaning, the best dielectric characteristics are shown at higher t-DCE concentration; however, the recommended t-DCE concentration is 5 w/o from the view point of balance of cost and performance. The high quality and highly reliable oxide film can be successfully formed by t-DCE added oxidation, which also minimizes the ozone layer influence. The t-DCE is a primary candidate to replace the 1,1,1-TCA.