We present a model that can be used to compute the charging and potential at any point of the electrochemical system comprising the ion-sensitive floating gate FET (ISFGFET) exposed to an electrolyte solution. In contrast to ion-sensitive FETs, the sensor has an additional control input gate. The model predicts the possibility for electrofluidic gating when the control gate (CG) is used in conjunction with a reference electrode (RE). Electrofluidic gating is the field-effect control over the electric double layer. We consider the applicability of electrofluidic gating in realizable devices and simulate the relationships between oxide properties and electrolyte solution to varying potentials of the CG and the RE. The oxide/electrolyte solution model is merged to the SPICE model of the transistor to create a unified model that can be used to simulate the transfer characteristics of the sensor in absolute terms to change input and electrolyte solution conditions. We simulate the sensor transfer characteristics with common Al2O3 surface to change the pH of the electrolyte solution and compare them to measurements. The results clarify the operation of ISFGFET and its applicability in electrofluidic gating.