Device isolation design rules for HAST improvement

Structures and methods for isolating semiconductor devices and improving device reliability under harsh environmental conditions are described. An isolation region may be formed by ion implantation in a region of semiconductor surrounding a device. The implantation region may extend into streets of a wafer. A passivation layer may be deposited over the implantation region and extend further into the streets than the isolation region to protect the isolation region from environmental conditions that may adversely affect the isolation region.