The present invention concerns a method of forming a chalcogenide thin film for a phase-change memory. In the method of forming a chalcogenide thin film according to the present invention, a substrate with a pattern formed is loaded into a reactor, and a source gas is supplied onto the substrate. Here, the source gas includes at least one source gas selected from germanium (Ge) source gas, gallium (Ga) source gas, indium (In) source gas, selenium (Se) source gas, antimony (Sb) source gas, tellurium (Te) source gas, tin (Sn) source gas, silver (Ag) source gas, and sulfur (S) source gas. A first purge gas is supplied onto the substrate in order to purge the source gas supplied onto the substrate, a reaction gas for reducing the source gas is then supplied onto the substrate, and a second purge gas is supplied onto the substrate in order to purge the reaction gas supplied onto the substrate. At least one operation, namely changing the supply time of the first purge gas and/or adjusting the internal pressure of the reactor is performed in such a way as to ensure that the deposition rate at an inner portion of the pattern is greater than the deposition rate at an upper portion of the pattern. According to the present invention, it is possible to form a chalcogenide thin film having an excellent gap-fill property by changing the purge time of the source gas or adjusting the internal pressure of the reactor in such a way as to ensure that the film forming rate at the inner portion of the pattern is greater than the film forming rate at the upper portion of the pattern.