Fluoxetine (FL) is one of the selective serotonin reuptake inhibitors, which is used as an anti-depressant, as well as anti-panic drug. In this work, a sensor for label-free recognition of trace amounts of FL is introduced, which is based on an extended gate field-effect transistor (EGFET). This sensor enables the detection and accurate measurement of FL concentrations over wide dynamic range. The sensing part of the device is a Pt electrode covered by a sensitive polyvinyl chloride (PVC) membrane. The functionalized Pt electrode acting as an extended gate of the EGFET, is connected to the internal gate of a MOSFET transducer. The sensing element of the PVC membrane is the insoluble ion-pair of FL cation and tetraphenylborate anion. The sensor performance for detection of FL was characterized in different ionic strengths of the matrix solution. Then, the sensor capability to operate in physiological phosphate-buffered saline (PBS) was assessed, where the sensor indicated two linear dynamic ranges of its response, with different sensitivities in 10(-11) -10(-5) M and 10(-5) -10(-3) M ranges. Also the calculated detection limit for the sensor was 2.63x10(-12) M. Moreover, the selectivity of the sensor was examined and validated in the presence of Citalopram, which is another anti-depressant drug with a similar structure to FL. We proposed a comprehensive analytical mapping of current sensitivity in all working regimes of the EGFET, providing a guide to the design of optimized sensors in any integrated systems of interest. Finally, the sensor was successfully exploited to assay citalopram in its pharmaceutical formulation.