A method for manufacturing a twin bit cell structure with an aluminum oxide material includes forming a gate dielectric layer overlying a semiconductor substrate and a polysilicon gate structure overlying the gate dielectric layer. An undercut region is formed in each side of the gate dielectric layer underneath the polysilicon gate structure. Thereafter, an oxidation process is performed to form a first silicon oxide layer on a peripheral surface of the polysilicon gate structure and a second silicon oxide layer on an exposed surface of the semiconductor substrate. Then, an aluminum oxide material is deposited over the first and second silicon oxide layers including the undercut region and the gate dielectric layer. The aluminum oxide material is selectively etched to form an insert region in a portion of the undercut region. A sidewall spacer is formed to isolate and protect the exposed aluminum oxide material and the polysilicon gate structure.