An apparatus for treating the substrate includes a process chamber with a treating space therein, a support member located in the treating space to support the substrate, and a gas supply unit supplying a surface-modifying gas to the treating space. The gas supply unit includes a bubbler tank provided with an accommodating space for storing a liquid alkyne-based chemical, the bubbler tanks bubbling the liquid alkyne-based chemical by supplying an inert gas to the accommodating space to generate the surface-modifying gas, a heater heating the liquid alkyne-based chemical stored in the bubbler tank at a first temperature, and a gas supply line coupled between the process chamber and the bubbler tank to supply the surface modified gas to the treating space and provided with a first valve.