Thermal flow sensor for determining the flow of a medium flowing in a flow direction, wherein four electrical resistors (A, B, C, D) are provided with a temperature-dependent electrical resistance, wherein said resistors are made from material that conducts cold, and wherein a control/evaluation unit is also provided, wherein the four resistors (A, B, C, D) are interconnected in a Wheatstone bridge, wherein the Wheatstone bridge is designed as one or more thin-film sensor elements and wherein the thin-film sensor element has a resistance structure, which is arranged on an electrically insulating substrate and which has a film thickness of 0.1 to 10 micrometers, wherein, during operation, the four resistors (A, B, C, D) are in thermal contact with the medium, wherein the control/evaluation unit is designed to supply an electrical current, during the measuring mode, to the Wheatstone bridge via two first non-adjacent conductor nodes (AC, BD; AD, BC) of the Wheatstone bridge, and wherein the control/evaluation unit is designed to measure the voltage (U out), which is present during the measuring mode, at two second non-adjacent conductor nodes (AD, BC; AC, BD) of the Wheatstone bridge, and to determine the flow from this, wherein a first membrane, which does not conduct heat, is arranged on the substrate, wherein the resistors (A, B, C, D) of the resistance structure are arranged on the first membrane in a predefined area of the substrate, and wherein, in the predefined area, the substrate is lowered by a predefined gap (h) in a direction that is perpendicular to the surface of the substrate in such a way that the first membrane is freely suspended in the predefined area, and in such a way that the first membrane thermally insulates the resistors (A, D, C, B) from the substrate in the predefined area in the direction that is perpendicular to the surface of the substrate, characterized in that - the control/evaluation unit supplies a current to the Wheatstone bridge, said current being regulated to a constant, predefined value, and - in the event of a minor shift of the resistance structure of less than 10 % in relation to the common axis of symmetry, caused by variations in the fabrication, the shift causes - a first change in the length of the section of the resistance structure arranged on the first membrane in a first current path of the Wheatstone bridge and - a second change in the length of the section of the resistance structure arranged on the first membrane in a second current path of the Wheatstone bridge, wherein the resistance structure is arranged in relation to the membrane in such a way that the first change in the length and the second change in the length are equal. wherein four electrical resistors (A, B, C, D) are provided with a temperature-dependent electrical resistance, wherein said resistors are made from material that conducts cold, and wherein a control/evaluation unit is also provided, wherein the four resistors (A, B, C, D) are interconnected in a Wheatstone bridge, wherein the Wheatstone bridge is designed as one or more thin-film sensor elements and wherein the thin-film sensor element has a resistance structure, which is arranged on an electrically insulating substrate and which has a film thickness of 0.1 to 10 micrometers, wherein, during operation, the four resistors (A, B, C, D) are in thermal contact with the medium, wherein the control/evaluation unit is designed to supply an electrical current, during the measuring mode, to the Wheatstone bridge via two first non-adjacent conductor nodes (AC, BD; AD, BC) of the Wheatstone bridge, and wherein the control/evaluation unit is designed to measure the voltage (U out), which is present during the measuring mode, at two second non-adjacent conductor nodes (AD, BC; AC, BD) of the Wheatstone bridge, and to determine the flow from this, - the control/evaluation unit supplies a current to the Wheatstone bridge, said current being regulated to a constant, predefined value, and - in the event of a minor shift of the resistance structure of less than 10 % in relation to the common axis of symmetry, caused by variations in the fabrication, the shift causes - a first change in the length of the section of the resistance structure arranged on the first membrane in a first current path of the Wheatstone bridge and - a second change in the length of the section of the resistance structure arranged on the first membrane in a second current path of the Wheatstone bridge,