A method includes receiving instructions for designing a ROM array, generating netlists for the ROM array, generating a data file representing a physical layout of the ROM array on a semiconductor wafer, and storing the data file in a computer readable storage medium. The instructions for the ROM array define a layout for a first unit including a first bit cell coupled to a first word line, a bus that may be coupled and uncoupled to a first power supply having a first voltage level, a layout for a second unit coupled to a second word line, and a layout for a third unit having an isolation device and being configured to share a bit line contact with the second unit or another third unit. The layout for the second unit is configured to be arranged at an edge of the ROM array and includes a dummy device.