Place all ingredients (except the rosemary) into a large plastic bag or medium sized bowl. Combine and coat. Let marinate for at least 30 minutes up to 24 hours.
Remove the leaves from the rosemary sprigs to create rosemary skewers.
Place the shrimp, tomatoes and onion onto the rosemary skewers. I prefer 2 shrimp for each skewer.
Place the rosemary skewers onto the grill. Cook about 3 minutes per side, for a total of 6 minutes. Remove and serve hot or place in the fridge and serve cold.
Notes
Be sure to examine the rosemary before you purchase. You will need thick rosemary branches to create a skewer from its branches.