Silicon carbide has robust mechanical, electrical, and chemical properties which make it an attractive material candidate for micro- and nano-electromechanical systems (MEMS and NEMS). 3C-SiC films grown via a polysilicon seed-layer CVD-deposited on an oxide coated (111) Si substrate offers an innovative method to overcome the residual film stress issues associated with 3C-SiC heteroepitaxy and the difficulties of fabricating structures from 3C-SiC films. The oxide plays a dual role by permitting film relaxation with respect to the supporting substrate and functioning as a MEMS release layer, allowing MEMS structures such as cantilevers and diaphragms, to be easily fabricated from the 3C-SiC film. The impact of the oxide layer on the relaxation of the film stress was investigated by comparing direction-sensitive MEMS stress sensors fabricated from 3C-SiC films grown via a polysilicon-on-oxide-coated-substrate and a polysilicon-on-crystalline Si substrate. Scanning Electron Microscopy (SEM) analysis of bridge structures fabricated on the polysilicon-on-oxide substrate revealed evidence of film strain relaxation when compared to bridge structures fabricated on the polysilicon-on-crystalline Si substrate. However, the upward-curled cantilever and comb structures fabricated on both substrates indicate the presence of a strain gradient in the 3C-SiC film grown on both substrates.