A thermal chemical vapor deposition (CVD) system includes a bottom chamber, an upper chamber, a workpiece support, a heater and at least one shielding plate. The upper chamber is present over the bottom chamber. The upper chamber and the bottom chamber define a chamber space therebetween. The workpiece support is configured to support a workpiece in the chamber space. The heater is configured to apply heat to the workpiece. The shielding plate is configured to at least partially shield the bottom chamber from the heat.