Abstract: A geothermal heat flux transducer includes a plurality of insulating slats on which constantin wire is wound and each half turn is coated with a silver layer to produce a hot junction and a cold junction per turn of wire. The slat with wire thus coated is assembled with insulating material between adjacent slats such that silver coatings on adjacent slats face each other and also uncoated wire half turns on adjacent slats face each other. This allows a multiplicity of thermal junctions thus formed to be assembled in a small package which may be suspended in earth bore holes in mine shafts or otherwise below or above ground for measurement of heat flow emanating from sources far below the earth's surface. Variable heat flow occasioned by diurnal and/or seasonal variations are accounted for in ascertainment of that steady heat flux flowing from geothermal sources alone. The transducer is of special dimensional proportions with parts specially related both structurally and thermally.