Preheat oven to 475°. Season chicken with salt and pepper. Heat oil in a 12' cast-iron or heavy nonstick skillet over high heat until hot but not smoking. Nestle chicken in skillet, skin side down, and cook 2 minutes. Reduce heat to medium-high; continue cooking skin side down, occasionally rearranging chicken thighs and rotating pan to evenly distribute heat, until fat renders and skin is golden brown, about 12 minutes.