The design and simulation of an electrochemical equivalent circuit for an extended-gate field-effect transistor (EGFET)-based pH sensor was presented in this paper. The pH sensor is essential in various fields, such as biomedical applications, environmental monitoring, and industrial processes. The proposed sensor utilized the EGFET structure to measure pH with high sensitivity and precision. In this study, an electrochemical equivalent circuit was developed to model the EGFET pH sensor behavior. The circuit comprised various components, including resistors, capacitors, and voltage sources, representing the electrical characteristics of the pH sensor. The circuit was simulated using LTSPICE XVII, a widely-used electronic circuit simulator. Experimental values obtained from actual pH measurements are utilized to validate the accuracy of the proposed electrochemical equivalent circuit. The simulated results are compared against the experimental data to ensure the circuit accurately captured the behavior of the pH sensor. The simulation allowed for a detailed analysis of the sensor performance under different pH conditions and optimized the sensor design parameters. It was found that the experimental transfer and output characteristics of the EGFET were very similar to those from the simulation program with integrated circuit emphasis (SPICE) simulation, and gate-to-source voltage (VGS) value at 3 V exhibited the value of drain current, ID at 234.002 μA, which is similar to the transfer characteristic of CD4007UBE using semiconductor device analyzer (SDA). Other than that, the changes in value components in the equivalent circuit did not affect the transfer and output characteristics graph. Still, the capacitor value produced significant output variation in the simulation. This can be related to the modification on the equivalent circuit with additional voltage, source to bulk (VSB), to produce the different threshold voltage (VT) values at different pH.