Prep the oven and pan. Heat the oven to 425°F (220°C).
Line a rimmed sheet pan with foil and set a wire rack on top if you have one. The rack helps air circulate for crispier skin.
Dry the chicken well. Pat the thighs thoroughly with paper towels, especially the skin. Removing surface moisture is key to getting a crunchy crust.
Mix the dry coating. In a small bowl, combine ranch seasoning, salt, pepper, garlic powder, paprika, cornstarch, and baking powder.
Taste a pinch of the mix; it should be zippy and savory.
Oil and season. Drizzle the thighs with oil and rub to coat lightly. Sprinkle the seasoning blend evenly on both sides, focusing extra on the skin. Press it on so it adheres.
Arrange on the pan. Place thighs skin-side up on the rack or directly on the foil.
Leave a little space between pieces so heat can flow around them.
Roast until crisp and golden. Bake for 35–45 minutes, depending on size. The skin should be browned and crackly, and an instant-read thermometer in the thickest part should read at least 175°F for super-tender thighs.
Optional broil for extra crunch. If you want even more crispness, broil for 1–3 minutes at the end. Watch closely to avoid scorching.
Rest and finish. Let the chicken rest 5 minutes.
Squeeze fresh lemon over the top and sprinkle with chopped parsley or chives for brightness.
Serve. Pair with roasted potatoes, corn on the cob, a green salad, or steamed green beans. The ranch flavor plays nicely with just about anything.