A method of forming a semiconductor structure includes: attaching a semiconductor device to a first surface of a substrate; placing a thermal interface material (TIM) film over a first side of the semiconductor device distal from the substrate, where the TIM film is pre-formed before the placing, where after the placing, a peripheral portion of the TIM film extends laterally beyond sidewalls of the semiconductor device; and attaching a lid to the first surface of the substrate to form an enclosed space between the lid and the substrate, where after attaching the lid, the semiconductor device and the TIM film are disposed in the enclosed space, where a first side of the TIM film distal from the substrate contacts the lid.