The structural characteristics of 3C-SiC mesastructures, realized by selective epitaxy on prestructured Silicon-On-Insulator (SOI) substrates using methylsilane, are studied by Transmission Electron Microscopy (TEM). It is shown that the quality of the film is comparable with the material grown under the standard conditions. The occurance of lateral growth at the edges of the 3C-SiC structures is limited by the layer-thickness. Loss of the oxide mask during the SiC deposition is observed and attributed to the decomposition of SiO(2).