In a mass flow sensor having a layered structure on the upper side of a silicon substrate (1), and having at least one heating element (8) patterned out of a conductive layer in the layered structure, thermal insulation between the heating element (8) and the silicon substrate (1) is achieved by way of a silicon dioxide block (5) which is produced beneath the heating element (8) either in the layered structure on the silicon substrate (1) or in the upper side of the silicon substrate (1). As a result, the sensor can be manufactured by surface micromechanics, i.e. without wafer back-side processes.