Semiconductor devices and electronic systems including the same

A method of fabricating a semiconductor device, the method comprising:

• forming a first mold structure, in which sacrificial layers and insulating layers are alternately stacked, on a substrate;
• forming second sacrificial patterns in first channel holes penetrating the first mold structure;
• forming a second mold structure on the first mold structure;
• forming trenches to penetrate the first and second mold structures;
• forming first sacrificial patterns in the trenches;
• forming a first supporting layer on the second mold structure and the first sacrificial patterns;
• forming second channel holes to penetrate the second mold structure and to expose the second sacrificial patterns;
• removing the second sacrificial patterns;
• forming vertical structures to penetrate the first supporting layer and the first and second mold structures;
• forming a second supporting layer on the first supporting layer and on the vertical structures;
• forming openings to penetrate the first and second supporting layers and to expose the first sacrificial patterns;
• removing the first sacrificial patterns through the openings;
• and
• replacing the sacrificial layers with electrodes.