The radiation sensing field effect transistor (RadFET) with SiO2 gate oxide has been commonly used as a device component or dosimetry system in the radiation applications such as space research, radiotherapy, and high-energy physics experiments. However, alternative gate oxides and more suitable packaging materials are still demanded for these dosimeters. HfO2 is one of the most attractive gate oxide materials that are currently under investigation by many researchers. In this study, Monte Carlo simulations of the average deposited energy in RadFET dosimetry systems with different package lid materials for point electron and photon sources were performed with the aim of evaluating the effects of package lids on the sensitivity of the RadFET by using HfO2 as a gate dielectric material. The RadFET geometry was defined in a PENGEOM package and electron-photon transport was simulated by a PENELOPE code. The relatively higher average deposited energies in the sensitive region (HfO2 layer) for electron energies of 250keV-20MeV were obtained from the RadFET with the Al2O3 package lid despite of some deviations from the general tendency. For the photon energies of 20-100keV, the average amount of energy deposited in RadFET with Al2O3 package was higher compared with the other capped devices. The average deposited energy in the sensitive region was quite close to each other at 200keV for both capped and uncapped devices. The difference in the average deposited energy of the RadFET with different package lid materials was not high for photon energies of 200-1200keV. The increase in the average deposited energy in the HfO2 layer of the RadFET with Ta package lid was higher compared with the other device configurations above 3MeV.