Electrical characteristics of trench capacitors using RTO (Rapid Thermal Oxidation) oxides, nitroxides, and reoxidized nitroxides as the gate insulators are discussed. High temperature RTO is effective in preventing oxide thinning at the trench corner, and so the dielectric strength of trench capacitors is improved drastically. The mean time to failure (MTTF) of trench capacitors using RTO is more than ten times longer than that of trench capacitors using conventional furnaces. Using reoxidized nitroxides as the gate insulator, superior charge to breakdown (QBD) is obtained. RTP (Rapid Thermal Processing) is superior to the process using the conventional furnace for the gate insulators of trench capacitors. Improvements in temperature uniformity, repeatability, and lessening of slip line formation are essential for RTP equipment to be practical.