Semiconductor devices with contact holes self-aligned in two directions

A semiconductor device comprising:

• a semiconductor substrate;
• a plurality of device isolation layers defining active regions on the semiconductor substrate;
• a plurality of gate structure patterns having gates and first mask patterns stacked on the semiconductor substrate, the gate structure patterns being spaced apart from each other and extending in a first direction;
• an interlayer insulating layer covering the gate structure patterns;
• a contact plug in a contact hole through the interlayer insulating layer that exposes the semiconductor device, wherein the contact hole includes a first contact hole provided at least between the first mask patterns and beneath the first mask patterns and a second contact hole provided in an upper portion of the first mask patterns in contact with the first contact hole;
• wherein the first contact hole has a first sidewall self-aligned to a surface of the first mask pattern in the first direction, a second sidewall self-aligned to a surface of a neighboring first mask pattern facing the first sidewall and parallel thereto, a third sidewall provided in a second direction crossing the first direction, and a fourth sidewall spaced apart from the third sidewall and parallel thereto;
• and
• wherein the second contact hole having a fifth sidewall outside the first sidewall, a sixth sidewall outside the second sidewall, and the third and fourth sidewalls, the second contact hole extending in the second direction.