The invention relates to the determination of the gas pressure in an evacuated thermal insulating board (9) having an insulating core (1) covered by a film (2). The inventive device comprises an assembly, which is integrated between the insulating core and the covering film of the thermal insulating board and which has a body that acts as a heat sink (3) (Al, Co, Fe, ceramic), and the body's thermal conductivity and thermal capacity relative to volume are greater than those of the insulating core. Said assembly also comprises a test layer (4) (0.3 mm nonwoven fabric made of plastic and glass fibers), which is arranged between the heat sink and the covering film and has a defined thermal conductivity that changes according to the gas pressure inside the evacuated thermal insulating board. From the exterior, a sensor device is applied to or pressed against the test device, which is placed inside the evacuated thermal insulating board and which is covered by the covering film. Said sensor device comprises a body (5) (coppered steel 78.degree. C., thermoelement (6)) having a distinctly different temperature than that of the test device (heat sink) whereby creating a heat flux, which is influenced by the thermal conductivity of the test layer, said thermal conductivity varying according to the gas pressure inside the thermal insulating board, and the magnitude of this heat flux is metrologically determined. The heat sink (3) can be provided in the form of a bottom part of a container for a getter material.