Structures and a method for detecting ionizing radiation using silicon-on-insulator (SOI) technology are disclosed. In one embodiment, the invention includes a substrate having a buried insulator layer formed over the substrate and an active layer formed over the buried insulator layer. Active layer may be fully depleted. A transistor is formed over the active layer, and includes a first gate conductor, a first gate dielectric and source/drain diffusion regions. The first gate conductor may include a material having a substantially (or fully) depleted doping concentration such that it has a resistivity higher than doped polysilicon such as intrinsic polysilicon. A second gate conductor is formed below the buried insulator layer and provides a second gate dielectric corresponding to the second gate conductor. A channel region between the first gate conductor and the second gate conductor is controlled by the second gate conductor (back gate) such that it acts as a radiation detector.