Photodetectors are important components in automotive industry. Sensitivity, speed, responsivity, quantum efficiency, photocurrent gain and power dissipation are the important characteristics of a photodetector. We report a high performance photodetector based on GaAs Metal- Semiconductor Field Effect Transistor (MESFET), with very high responsivity, excellent quantum efficiency, high sensitivity, moderate speed, tremendous gain and low power dissipation, surpassing their photodiode, phototransistor and other counterparts. A theoretical model of GaAs front illuminated Optical Field Effect transistor is presented. The photovoltaic and photoconductive effects have been taken into account. The gate of the OPFET device has been left open to make a reduction in the number of power supplies. The results are in line with the experiments. The device shows high potential in automotive applications.