Through a novel methodology for evaluating layer-by-layer residual stresses in epitaxial silicon carbide films with resolution down to 10 nm, we indicate the existence of a highly compressed interfacial nanolayer between the films and their silicon substrates. This layer is consistently present underneath all types of silicon carbide films examined herein, regardless of the extent of residual tensile stress measured in the full thickness of the films, which varies from 300 up to 1300 MPa. We link this nanolayer to the carbonization step of the film growth process and we discuss in detail the implications in terms of fracture behaviour by bulge testing of micromachined membranes.