A novel MOSFET-based dosimeter that uses a floating polysilicon gate to trap radiation-generated charge is reported. As in previous MOSFET dosimeters, absorbed dose is inferred from changes in threshold voltage. High sensitivity is obtained by extending the floating gate over the field oxide. Prototype devices have been fabricated in a conventional 5 μm nMOS integrated-circuit technology, and show sensitivities up to 280 mV Gy-1 when irradiated with a 60Co gamma source.