Low resistivity and diffusivity of epitaxial films of TiN (a=4.24Å) on Si (a=5.43Å) and GaAs (a=5.65Å) make these films excellent choice as barrier layers in VLSI metalization. Epitaxial structural relationships at the interface in large mismatch systems, such as TiN/Si and TiN/GaAs were investigated by transmission electron microscopy, and multi-slice simulation technique. Studies wereperformed on TOPCON 002B high resolution microscope operated at 200 kV, with resolution limit at 1.8Å. Computer simulations with image processing was carried out on IBM/PC-AT computer incombination with IBAS/IPS image processing system of KONTRON electronic group. Epitaxial (100)TiN films on Si(100) and (110)TiN films on GaAs(100) have been deposited by laser physical vapor deposition.From the SAED patterns the orientation relationships have been found to be cube-on-cube for the TiN/Si interface i.e. <100>TiN//>100>Si (Fig.l); and [001]TiN//[110]GaAs and [10]TiN//[10]GaAs (Fig.2a,b). The analysis of the diffraction data for the TiN/GaAs interface reveals that TiN unit cell is rotated twice by 45° - with respect to [001] GaAs and with respect [110] GaAs (Fig.3). Thus the coordinates of the TiN unit cell axes a', b', and c' are expressed in the bases of GaAs axes a,b,c as: a'= -0.375a + 0.375b + 0.531c; b'= 0.375a - 0.375b + 0.531c; and c'= 0.531a + 0.531b.