In this study, an efficiency of 43.4% ± 2.4%abs for the direct conversion of sunlight into electricity has been demonstrated with a CPV subunit device. This subunit consists of a 4J solar cell and an achromatic full-glass lens. 43.4% is the highest reported CSTC efficiency in CPV application so far. The measurement uncertainty of ±2.4%abs is calculated following [16]. The aperture area of this subunit is 18.2 cm2 and achieves a geometrical concentration of 340×. The CSOC efficiency is 42.5%. The reason for this high efficiency is the combination of a highefficiency solar cell (46%) and a high-efficiency lens (95%). Furthermore, the I–V curve of the solar cell has been measured for varying distances to the glass lens. These measurements are compared with measurement done with a SoG Fresnel lens.