Amorphous silicon carbonitride (SiCN) ceramics were synthesized by pyrolyzing a polysilazane at different temperatures between 900° and 1400°C. The microstructures and compositions of the materials obtained were analyzed using X-ray diffraction, elemental analysis, and Raman spectroscopy. To study their piezoresistive behavior, the resistivity of the resultant materials were measured as a function of applied stress. We found that the piezoresistive behavior of all materials can fit the tunneling-percolation model. The piezoresistive stress coefficient of the materials obtained at temperatures below 1200°C showed both reverse and logarithmical dependences on applied stress, but that of the materials obtained at higher temperatures showed only logarithmical dependence. We believe that the pyrolysis temperature induces a change in the free carbon structure thus, causing this effect on the piezoresistivity.