We investigate the microstructure of 3C-SiC by both conventional and high resolution transmission electron microscopy. The samples were grown by the modified Lely-method at temperatures between 1850-1950 degreesC using 3C-SiC seed crystals grown on undulating silicon. Our investigations show that growth is predominantly cubic. However, transmission electron microscopy reveals that the material contains bands of several micrometer thickness that consist of stacking faults in high density. High resolution transmission electron microscopy shows in addition that these stacking faults are irregularly spaced with maximum densities of one stacking fault every three bilayers. In some small regions the stacking faults have regular spacing and form 6H nanoinclusions with a thickness of up to 15 bilayers. The presence of 6H in these regions could also be confirmed by electron diffraction patterns. In addition we detect macroscopic 6H inclusions with several micrometer thickness.