In a small bowl, whisk together the rosemary, thyme, oregano, garlic powder, salt, and pepper. Note: The rosemary can be crushed with your fingers or the back of a wooden spoon if you don't want large rosemary leaves on your chicken--this is completely up to you.
Rinse and pat the chicken dry. Sprinkle each piece of chicken (the top of the chicken thighs) with the seasoning.
Add the oil to a large cast iron skillet. Heat the skillet over medium-high heat. Once the skillet is hot, add the chicken so the top of the chicken is facing down in the skillet. The oil should sizzle as soon as you place the chicken in the skillet. If the oil doesn't sizzle, your skillet isn't hot enough yet to add the chicken. Cook the chicken for 6 minutes. After about 6 minutes, the skin (and chicken) should easily pull away from the skillet. If the skin doesn't pull away from skillet, cook the chicken for a minute or two longer. Flip the chicken and cook for 5-6 minutes.
Transfer the skillet (and chicken) to the hot oven. Cook the chicken for about 30 minutes, or until cooked all the way through (165F).