An apparatus for determining the temperature of a substrate, in particular of a semiconductor substrate during its heating, the apparatus comprising: - at least one first radiation source for heating the substrate; - a first radiation detector, which is directed onto a first surface area of the substrate, which surface area faces towards the at least one radiation source, such that radiation emitted by the substrate and a first proportion of radiation of the at least one radiation source, which is reflected at the substrate, falls onto the first radiation detector (20, but in substance no radiation stemming directly from the at least one radiation source, - a second radiation detector, which is directed onto a second surface area of the substrate, which second surface area faces to the at least one radiation source, such that radiation emitted by the substrate and a second proportion of radiation of the at least one radiation source, which is reflected at the substrate, falls onto the second radiation detector, but in substance no radiation stemming directly from the at least one radiation source, wherein the first and second proportions of the radiation of the first radiation source, which is reflected at the substrate, which fall onto the respective radiation detectors (20, 21), are different, wherein the first and second radiation detectors detect in substance the same substrate-radiation, and wherein the first and second surface areas (20a, 21a) are substrate areas having in substance the same temperature; and - a temperature determination unit, which is configured to determine the temperature of the substrate directly based on a drive power or radiation intensity of the first radiation source and the radiation detected by the first and second radiation detectors (20, 21). - at least one first radiation source for heating the substrate; - a first radiation detector, which is directed onto a first surface area of the substrate, which surface area faces towards the at least one radiation source, such that radiation emitted by the substrate and a first proportion of radiation of the at least one radiation source, which is reflected at the substrate, falls onto the first radiation detector (20, but in substance no radiation stemming directly from the at least one radiation source, - a second radiation detector, which is directed onto a second surface area of the substrate, which second surface area faces to the at least one radiation source, such that radiation emitted by the substrate and a second proportion of radiation of the at least one radiation source, which is reflected at the substrate, falls onto the second radiation detector, but in substance no radiation stemming directly from the at least one radiation source, wherein the first and second proportions of the radiation of the first radiation source, which is reflected at the substrate, which fall onto the respective radiation detectors (20, 21), are different, wherein the first and second radiation detectors detect in substance the same substrate-radiation, and wherein the first and second surface areas (20a, 21a) are substrate areas having in substance the same temperature; and - a temperature determination unit, which is configured to determine the temperature of the substrate directly based on a drive power or radiation intensity of the first radiation source and the radiation detected by the first and second radiation detectors (20, 21).