By means of electron microscopy, a comparative analysis of the micro-inhomogeneous structure of the surface of films of amorphous aromatic polyetherimide — poly{4,4'-bis[(4''-N-phenoxy) diphenylsulfone] imide 1,3-bis (3',4-dicarboxyphenoxy) benzene} (PEI) - and imidosiloxane block copolymer (PSI) containing blocks of PEI units and blocks of dimethylsiloxane units. It is shown that in the PSI film, compared with PEI, the anisotropy, long-range order, and the correlation length of density fluctuations increase. The PSI sample has an asymmetrical biaxial surface texture, unlike PEI, which is characterized by an axial texture. In the direction of the axes of the PSI texture on a micron scale, periodic density oscillations are observed. The results obtained indicate microphase separation in the PSI film due to spatially oriented contact interactions between the blocks of dimethylsiloxane units.