Semiconductor memory devices having variable resistor and methods of fabricating the same

According to a method of fabricating the semiconductor memory device, a contact plug can be protected while mold openings are formed. A semiconductor memory device may include a mold dielectric layer on an entire surface of a substrate, the substrate including a first region and a second region. A contact plug may be provided in a contact hole formed through the mold dielectric layer in the first region. A variable resistor may be provided in a mold opening formed through the mold dielectric layer in the second region. An upper surface of the contact plug may be at a level equal to or lower than an upper surface of the mold dielectric layer.