Place a layer of onion in the bottom of a pressure cooker. Add a layer of ribs. Repeat with remaining onion and ribs.
Combine barbeque sauce and broth together in a bowl; pour over ribs in the pressure cooker.
Close cooker securely and place pressure regulator over vent according to manufacturer's instructions. Heat until steam escapes in a steady flow and makes a whistling sound, about 5 minutes. Adjust heat until regulator is gently rocking. Cook for 25 minutes. Transfer the pressure cooker to the sink; cool the pot with cold water for about 30 seconds to release pressure quickly.