This work presents a two-dimensional numerical simulation study of pentacene organic thin-film transistors (OTFTs). Analyzing the influence of pentacene thickness on key device characteristics. Simulations were performed using Silvaco ATLAS to systematically evaluate the effect of decreasing the organic semiconductor (OSC) thickness from 50 nm to 10 nm. Critical electrical parameters such as threshold voltage (Vth), ON-current (ION), OFF-current (IOFF), ION/OFF ratio, transconductance (gm), and subthreshold slope (SS) were extracted and analyzed. The results reveal that these parameters are significantly influenced by changes in the active layer thickness. The ION/IOFF ratio shows strong dependence on the semiconductor thickness, with the highest ION/IOFF ratio observed at 10 nm to 50 nm, making it particularly suitable for high-speed switching applications in digital circuits. This study emphasizes the importance of thickness optimization for enhancing OTFT performance, paving the way for their integration into practical low-power electronic applications such as Organic Transistors Using Flexibility for Biosensing, flexible displays, sensors, and RFID systems.