The invention relates to a device for detecting thermal radiation (3), comprising at least one thermal detector element (2) that converts the thermal radiation into an electric signal (4). The inventive device is further provided with at least one focusing element (12) that focuses the thermal radiation onto the detector element. The focusing element is for example a lens that consists of a semiconducting material such a silicon. Preferably, the focusing element is integrated in the detection window for detecting the thermal radiation, said detection window consisting of a semiconducting material.