An apparatus for determining the temperature of a substrate (W), 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 (W), 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 (W), 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 , are different, wherein the first and second radiation detectors detect in substance the same substrate-radiation, and wherein the first and second surface areas are substrate areas having in substance the same temperature; and - a temperature determination unit, which is configured to determine the temperature of the substrate (W) 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 . - 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 (W), 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 (W), 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 , are different, wherein the first and second radiation detectors detect in substance the same substrate-radiation, and wherein the first and second surface areas are substrate areas having in substance the same temperature; and - a temperature determination unit, which is configured to determine the temperature of the substrate (W) 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 . <EOS>