Heat oven to 425°F. Line a sheet pan with foil and set a wire rack on top.
Pat chicken dry with paper towels and trim extra skin or fat.
Combine baking powder, garlic powder, onion powder, smoked paprika, thyme, salt, and pepper in a small bowl.
Drizzle chicken with olive oil and rub to coat. Sprinkle on the seasoning and rub under the skin, too.
Arrange thighs on the rack, skin-side up, leaving space between pieces.
Bake 30–35 minutes, until skin is crisp and the thickest part reaches 175°F. Broil 2–3 minutes for extra crunch if desired.
Rest 5 minutes. Sprinkle with parsley and serve.