The invention relates to a sensor unit (2) for determining the core body temperature by means of measured values which can be determined outside the body on a surface, comprising at least one heat flow sensor (20, 20′；), and at least one temperature sensor (21, 21′；), which can be easily compactly produced and installed and allows optimized determination of the core body temperature. This is achieved in that the sensor unit (2) comprises at least one monolithic heat flow sensor (20, 20′；) in the form of a sandwich-like structure consisting of multiple layers of different materials and at least one temperature sensor (21, 2′；), which are soldered unto a circuit board (22) at a distance from one another or onto the circuit board (22) at the same height along a longitudinal direction of the circuit board (22), wherein the sensors (20, 21) are connected to an analog-to-digital convener (25) and a microcontroller (26) via wires or strip conductors, the electronic components (20, 21, 25, 26) can be connected to the electronics of a portable computer system by means of connecting wires (3), and the sensor unit (2) or the circuit board (22) with electronic components (20, 21, 25, 26) arranged thereon is at least partially enclosed by a sensor unit sleeve (28) in the transverse direction of the circuit board (22).
