Gamma-ray dosimeter is an instrument which measures dose amount attracted by gamma ray. This integrated sensor is utilized for high irradiation and low sensitivity applications such as blood sterilization. In this article, a gamma-ray MOSFET dosimeter including a floating-gate MOSFET transistor as a sensor and a gate connection reference transistor with identical geometry are simulated using the TSMC 0.13-micron process technology. Floating-gate transistor is used in low-power circuits. The dosimeter applied herein makes use of general dose measurement methodology. Source of gamma ray is cobalt-60. Here, the impact of transistor gate’s thickness of floating transistor served as a sensor on sensitivity of dosimeter is examined. To do so, dosimeter was simulated using the software HSPICE, and impact of different thicknesses of floating transistors on sensitivity was examined. Finally, it was concluded that an increase in transistor gate’s thickness of floating transistor would bring about an improvement of at least 25 percent in sensitivity.