Depositing high-quality tunneling layers for two-dimensional (2D) floating gate transistors remains challenging, as it requires precise process control and parameter optimization. Herein, we fabricated a floating gate structure incorporating a high-quality hafnium oxide (HfO_x) tunneling layer achieved via ozone-induced oxidation of HfS₂ flakes. This process forms a nano-confined elemental oxygen layer at the tunneling layer/channel interface, which effectively suppresses leakage current. As a result, the WSe₂ floating gate transistor exhibits exceptional memory performance, including a high programming/erasing ratio, a long retention time (10⁵ s), multibit storage capacity, and reliable low temperature operation. Leveraging its programmable characteristics and robust performance, we demonstrated logic-in-memory operations with functional NOT, XNOR, and XOR gates. This rationally designed floating gate structure offers a promising approach for high-performance memory devices and logic-in-memory systems.