Combine balsamic vinegar with extra virgin olive oil then season with minced garlic, thyme, pepper, and chopped rosemary.
Rub the chicken thighs with the spice mixture then let it rest for approximately 15 minutes.
In the meantime, preheat a grill over medium heat then wait until it is ready.
Place the seasoned chicken thighs on the grill then grill until all sides of the chicken are golden brown and cooked through. Brush the chicken thighs with the marinade once every 5 minutes.
Once it is done, remove the chicken from the grill and transfer to a serving dish.