Disclosed herein are IC structures, packages, and devices that include III-N transistors integrated on the same support structure as non-III-N transistors (e.g., Si-based transistors), using semiconductor regrowth. In one aspect, a non-III-N transistor may be integrated with an III-N transistor by depositing a III-N material, forming an opening in the III-N material, and epitaxially growing within the opening a semiconductor material other than the III-N material. Since the III-N material may serve as a foundation for forming III-N transistors, while the non-III-N material may serve as a foundation for forming non-III-N transistors, such an approach advantageously enables implementation of both types of transistors on a single support structure. Proposed integration may reduce costs and improve performance by enabling integrated digital logic solutions for III-N transistors and by reducing losses incurred when power is routed off chip in a multi-chip package.