For stretchable electronics to achieve broad industrial application, they must be reliable to manufacture and must perform robustly while undergoing large deformations. We present a new strategy for creating planar stretchable electronics and demonstrate one such device, a stretchable microelectrode array based on flex circuit technology. Stretchability is achieved through novel, rationally designed perforations that provide islands of low strain and continuous low-strain pathways for conductive traces. This approach enables the device to maintain constant electrical properties and planarity while undergoing applied strains up to 15%. Materials selection is not limited to polyimide composite devices and can potentially be implemented with either soft or hard substrates and can incorporate standard metals or new nano-engineered conductors. By using standard flex circuit technology, our planar microelectrode device achieved constant resistances for strains up to 20% with less than a 4% resistance offset over 120,000 cycles at 10% strain.