A selenization/sulfurization process apparatus for use with a single-piece glass substrate is characterized by two chambers for heating up a glass substrate quickly and performing selenization/sulfurization on the glass substrate to not only prevent the glass substrate from staying at a soaking temperature of a softening point for a long period of time but also increase the thin-film selenization/sulfurization temperature according to the needs of the process to thereby reduce the duration of soaking selenization/sulfurization, save energy, and save time. The glass substrate undergoes reciprocating motion in the chambers to not only attain uniform temperature throughout the glass substrate but also distribute a selenization/sulfurization gas across the glass substrate uniformly during the selenization/sulfurization operation. The recycled liquid selenium/sulfur and inert gas are reusable to thereby reduce material costs.