Abstract: A transistor having a gate dielectric layer of partial thickness difference and a method of fabricating the same are provided. The method includes forming a gate dielectric layer having a main portion with a relatively thin thickness formed on a semiconductor substrate, and a sidewall portion with a relatively thick thickness formed on both sides of the main portion. A first gate is formed overlapping the main portion of the gate dielectric layer, and forming a second gate layer covering the sidewall portion of the gate dielectric layer and covering the first gate. The second gate layer is etched, thereby forming second gates patterned with a spacer shape on sidewalls of the first gate. The exposed sidewall portion of the gate dielectric layer is selectively etched using the second gates as a mask, thereby forming a pattern of the gate dielectric layer to be aligned with the second gates. A source/drain is formed in a portion of the semiconductor substrate exposed by the second gates.