Preheat oven to 400°F. Wash kale well. Use a sharp knife to remove the central rib in each leaf. Cut kale leaves into 2- to 3-inch pieces. Dry thoroughly in salad spinner. Place kale in large bowl. Drizzle with oil and sprinkle with rosemary and sea salt; toss to coat well.
Place kale in single layer on 2 large shallow foil-lined baking pans.
Bake one pan at a time for 15 minutes or until crisp, rotating pan halfway through cook time. Cool 1 to 2 minutes before serving.