The semimembranosus muscle is one of the three muscles that make up the hamstring. It is found on the back of the thigh and runs from the base of the pelvis (specifically the tuberosity of the ischium) to the back of the tibia, one of the bones that make up the lower leg. The semimembranosus muscle is attached to the pelvis and tibia via tendons.

The muscle has several functions, including enabling the leg to flex and rotate, and serving as a thigh extensor. The other two muscles that make up the hamstring are the semitendinosus and biceps femoris muscles.

An injury to the semimembranosus muscle is referred to as a hamstring injury. Treatment for hamstring injuries includes ice packs, stretching, massaging, and using the injured muscle as soon as possible after the injury. This helps promote the growth of new muscle fibers to replace those damaged by injury. Properly warming up and stretching before exercise or running will help prevent injury to this muscle.