Requests to have more compact, more robust and more sensitive photosensor are appearing in many physics applications. A novel type of avalanche photodetector with Geiger mode operation, known as Silicon PhotoMultiplier (SiPM) represents an interesting advance in photodetection and could soon be an alternative to traditional PMTs in many applications. The state of the art of the SiPMs - their main properties and problems will be discussed. Special note will be given on a specific development of those devices performed in the Max Planck Institute Semiconductor Laboratory in Munich.