Radiation sensing MOSFETs (RADFETs) have found numerous applications in space research, as well as in nuclear technology and research, and radiotherapy. Since proton irradiation is an essential part of the space radiation environment, it is important to know RADFET proton response precisely. In this work a numerical simulation of RADFET proton response is performed. To this end the proton transport Monte Carlo software SRNA-2K5, developed by one of the authors, has been adapted to obtain the energy deposited in the RADFET structure and dose distribution within the microscopic dimensions of the dosimeter sensitive volume. Our results show that RADFET response to proton irradiation depends significantly of packaging configurations with kovar lid.