A simple dosimeter design is described in which a thermoluminescent phosphor is mounted on an electrically heatable support in an evacuated or gas‐filled envelope. With CaF2:Mn as the phosphor, the device detects gamma‐ray doses in the milliroentgen range and is linear in response up to at least 2×105r. Dose readings can be made in less than a minute with simple instrumentation requiring no darkroom facilities. The dosimeter may be reused many times. The response is independent of dose rate at least over the range 10 mr/min to 7000 r/min. With suitable tin shields the response is independent of energy over the range 40 kev to 1.25 Mev. The advantages of this device for monitoring of personnel in health physics operations are pointed out.