Transmission electron microscopy was performed on a carbon-containing SiOC material derived from a polymer precursor pyrolyzed at 1100 degrees C and subsequently annealed at 1400 degrees C. The TEM study focused on the correlation between micro/nanostructure evolution and the piezoresistivity monitored on the annealed sample. Upon pyrolysis, the material was completely amorphous with no local crystallization of the thermodynamically stable phases. Upon annealing, however, the formation of turbostratic carbon and SiC was observed. Unexpectedly, crystallization only occurred within intrinsic pores while the bulk of the sample remained amorphous. As the nanopores formed a percolation network throughout the entire material, the piezoresistive effect is predominantly a consequence of turbostratic carbon formation inside the residual porosity.