Provided are methods of forming patterns of wafers using self-aligned double patterning processes. The methods include preparing an initial layout having a first design pattern, a second design pattern, and a third design pattern disposed between the first design pattern and the second design pattern, extracting a first sub-layout including the first design pattern and a second sub-layout including the second design pattern from the initial layout using a computer, forming a first modified sub-layout including a first modified design pattern obtained by modifying the first design pattern of the first sub-layout using the computer, generating a modified layout including the first modified sub-layout and the second sub-layout using the computer, and performing a double patterning process using the modified layout.