The semiconductor device comprises a semiconductor substrate (1), a sensor or sensor array (2) arranged at a main surface (10) of the substrate, an integrated circuit (3) arranged at or above the main surface, and a focusing element (17) comprising recesses (4) formed within a further main surface (11) of the substrate opposite the main surface. The focusing element may be arranged opposite the sensor or sensor array (2), which may be a photosensor or photodetector or an array of photosensors or photodetectors, for instance. The focusing element (17) is formed by etching the recesses (4) into the semiconductor material.