A low-cost sensing mechanism of hydrogen gas is developed using polymer-derived ceramic, a liquid organic precursor, polysilazane with the addition of 5wt% of photoinitiator, 2,2 Dimethoxy-2-phenyl acephenone. UV photopolymerization is utilized to partially cross-link the H-shaped free standing specimen, and then pyrolyzed at 1400 degrees C in hot isostatic press under nitrogen gas to convert the partially cross-linked polymer into conducting and amorphous ceramic, silicon carbonitride. This work presents the preparation of free standing silicon carbonitride specimens as the sensor body for sensing hydrogen gas, depending on the semiconductive behavior of polymer-derived ceramics in high-temperature environments. The band gap of silicon carbonitride would be varied from adsorbing hydrogen molecules on the surface of the H-shaped free standing specimen with two different thicknesses. An amenable specimen-geometry for the four-point test of measuring resistance is developed in a furnace filled with pure hydrogen and vacuumed environments.