Preheat your oven to 200°C (400°F).
Pat chicken thighs dry with a paper towel and place them in a baking dish.
Drizzle with olive oil, scatter lemon slices, garlic, and rosemary around.
Season generously with salt and black pepper.
Roast for 40 minutes until the skin is golden and the juices run clear.
Let rest for 5 minutes before serving with pan juices spooned over the top.