Langmuir-Blodgett films of mesomorphic side-chain poly(methacrylates) are investigated from the point of view of their phase change versus temperature via X-ray and neutron reflectivity together with atomic force microscopy measurements. Upon heating, "thick" films undergo an irreversible transition toward the well-known smectic A(1) lamellar phase. In contrast, a bilayer deposited onto a solid substrate appears to be very stable upon annealing. Such a behavior is believed to induce an epitaxial mechanism when cooling "thick" films from the isotropic melt phase.