Multilayer Si/Ge heterostructures with the thickness of Ge layers varying from 2 to 12 monolayers (ML) were formed by molecular beam epitaxy (MBE) on the (001) Si substrates at 300°C (Ge) and 450°C (Si). The study of the Si/Ge heterostructures was performed by transmission and Cs corrected scanning transmission electron microscopy (STEM). It was shown that the growth of Ge layers up to thickness of 5 ML occurs through the Frank-van der Merwe mechanism. For thicker Ge layers the growth mechanism of the Si-Ge heterostructure changes to Stranski-Krastanov with Si-Ge islands having the shape of inverted pyramids. The Si-Ge layer intermixing was discussed.