A straightforward improvement of the efficiency and long term stability of silicon dosimeters has been obtained with a n+-p junction surrounded by a guard-ring structure implanted on an epitaxial p-type Si layer grown on a Czochralski substrate. The sensitivity of devices made on 50-μm-thick epitaxial Si degrades by only 7% after an irradiation with 6 MeV electrons up to 1.5 kGy, and shows no significant further decay up to 10 kGy. These results prove the enhanced radiation tolerance and stability of epitaxial diodes as compared to present state-of-the-art Si devices.