General IGBTs are of two basic types, the planar IGBT and the trench IGBT. The trench IGBT has certain advantages when compared with the planar IGBT, such as a lower on-state voltage drop and a smaller cell pitch, but it also has a disadvantage in its lower breakdown voltage. The lower breakdown voltage is caused by the electric field being concentrated in a corner along the bottom of the trench gate. Therefore in this paper we propose a new trench IGBT structure that is designed to offer improved breakdown voltage. In this proposed structure, the narrow oxide strip beneath the trench gate where the electric field is concentrated is extended into a rectangular shape in order to decrease the electric field. This results in an increase in the breakdown voltage. Fabricating this structure is not complicated because the only step added to the conventional TIGBT fabrication process is an Epitaxial Lateral Overgrowth process to create the rectangular oxide. The electrical characteristics of the proposed structure are analyzed theoretically and also modeled using simulators, such as TSUPREM and MEDICI. These analyses indicate that the on-state voltage drop and the threshold voltage are similar to those in a conventional TIGBT but the breakdown voltage is improved by a factor of 23%.