A method of manufacturing a variable resistance memory device includes: forming an array of memory cells on a substrate, each memory cell including a variable resistance structure and a switching element; and forming a sidewall insulating layer covering a sidewall of the switching element. The forming the sidewall insulating layer includes: a preliminary step of supplying a silicon source to an exposed sidewall of the switching element; and a main step of performing a process cycle a plurality of times, the process cycle comprising supplying the silicon source and supplying a reaction gas, A time duration of the supplying the silicon source in the preliminary step is longer than a time duration of the supplying the silicon gas in the process cycle in the main step.