Using KETEK technology, First Sensor´s Silicon Photomultipliers are very precise state-of-the-art low level light detectors. They are suitable for many different applications like chemical analysis, medical diagnosis, scientific research and industrial measurement. Their peak sensitivity is at 420 nm to match with the LYSO scintillator emission peak in radiation detection applications. Besides the high photon detection efficiency the main features are low noise, large range of stable operation and an extremely low temperature coefficient of the gain.