A sensor unit adapted to measure a mass flow rate of a liquid hot-melt adhesive, comprising at least: a flow channel for the hot-melt adhesive, a first temperature measurement device positioned at a first position in the flow channel for measuring a temperature of the hot-melt adhesive at the first position in the flow channel, a second temperature measurement device positioned at a second position in the flow channel and a heating device assigned to the second temperature measurement device for heating the second temperature measurement device, the second temperature measurement device being used for measuring a second temperature at the second, heated temperature measurement device, and a control unit for controlling the heating device and for measuring the mass flow rate, which is designed and configured to adjust the temperature of the second temperature measurement device to a value and determine the heating power for heating the second temperature measurement device and to calculate the mass flow rate in the flow channel, characterized in that the sensor unit comprises: a sensor block, wherein 1) the first temperature measurement device and the second temperature measurement device are mounted on the sensor block; 2) the first temperature measurement device and the second temperature measurement device are each planar and flat; and 3) the first temperature measurement device and the second temperature measurement device are arranged substantially parallel to each other in the flow channel. a flow channel for the hot-melt adhesive, a first temperature measurement device positioned at a first position in the flow channel for measuring a temperature of the hot-melt adhesive at the first position in the flow channel, a second temperature measurement device positioned at a second position in the flow channel and a heating device assigned to the second temperature measurement device for heating the second temperature measurement device, the second temperature measurement device being used for measuring a second temperature at the second, heated temperature measurement device, and a control unit for controlling the heating device and for measuring the mass flow rate, which is designed and configured to adjust the temperature of the second temperature measurement device to a value and determine the heating power for heating the second temperature measurement device and to calculate the mass flow rate in the flow channel, characterized in that the sensor unit comprises: a sensor block, wherein 1) the first temperature measurement device and the second temperature measurement device are mounted on the sensor block; 2) the first temperature measurement device and the second temperature measurement device are each planar and flat; and 3) the first temperature measurement device and the second temperature measurement device are arranged substantially parallel to each other in the flow channel. 1) the first temperature measurement device and the second temperature measurement device are mounted on the sensor block; 2) the first temperature measurement device and the second temperature measurement device are each planar and flat; and 3) the first temperature measurement device and the second temperature measurement device are arranged substantially parallel to each other in the flow channel.