We present different aspects of the molecular beam epitaxy (MBE) growth of InAs QDs directly on silicon. At a substrate temperature of 370 degrees C and a growth rate of 0.25 ML/s we observe an abrupt transition from 2D to 3D growth mode after the deposition of nominally 1.7 hit of InAs, independent of the III/V flux ratio. The density of quantum dots, measured ex situ by atomic force microscopy (AFM), depends strongly on the BEP(In/As) and the amount of deposited InAs. We observed a maximum of 10(11) cm(-2) dots. Indium droplet formation for the,growth on silicon could be studied by using energy dispersive X-ray analysis. Furthermore, the silicon overgrowth has been studied. By in situ X-ray emission spectroscopy (XPS) we measured the temperature stability of a 3 nm Si-cap. At 400 degrees C Indium droplets are forming by In diffusion through the Si-cap layer.