The formation of single and multiple stacking faults that sometimes give rise to 3C-SiC was observed in a highly doped n-type 4H-SiC epilayer following thermal oxidation. Transmission electron microscopy following oxidation revealed single stacking faults and bands of 3C-SiC within a 4H-SiC matrix in the epilayer. In addition to the 3.22 eV photon energy peak corresponding to 4H-SiC, depth-resolved cathodoluminescence spectroscopy at 25 degreesC based on low energy-excited electron nanoscale luminescence revealed a spectral peak at 2.5 eV photon energy that was not present in the sample prior to oxidation. The polytypic transformation is tentatively attributed to the motion of Shockley partial dislocations on parallel (0001) slip planes. The generation and motion of these partials may have been induced by the stresses that were generated during oxidation, and/or the epilayer stresses generated by change in lattice constant due to its heavy doping.