An analysis was performed of the design of a thermal vacuum sensor. The sensor was made by the thin-film technique and consisted of a heating resistor and a thermopile, including six thermoelements. The surface of the heater has been covered with a reflective Al layer that significantly reduced the heat dissipated by radiation. In that way an increase in sensitivity and extending of the measurement range have been achieved. The effect of surface emissivity and sensor dimensions on its characteristics has been studied.