A method of modifying a power mesh includes measuring distances between end cap blocks included in a standard cell in a chip sub-block. The end cap blocks are located at edges of the chip sub-block and edges of the macro cell. The method includes searching a logic circuit block located between the first and second end cap blocks of the end cap blocks. A distance between the first and second end cap blocks is shorter than a predetermined length. It is determined whether a power supply voltage line and a ground voltage line exist at a partial region of the first power mesh layer. When the power supply voltage line or the ground voltage line is determined not to exist at the partial region, the power mesh data are modified to supplement the power supply voltage line or the ground voltage line at the partial region.