Hip-knee-ankle-foot (HKAF) prostheses are full lower limb devices for people with hip amputations. They are designed to enable individuals to regain their mobility and move freely with little restriction. HKAFs typically have high rejection rates among users, as well as gait asymmetry and increased trunk anterior-posterior lean and pelvic tilt. In this thesis, a novel integrated hip-knee (IHK) unit was designed and evaluated to address the limitations of existing solutions. This IHK combines powered hip and microprocessor controlled knee joints into one structure, with shared electronics, sensors, and batteries. The unit is also adjustable to the user leg length by a prosthetist. ISO-10328 standard mechanical testing demonstrated acceptable structural safety and rigidity. Successful functional testing involved three able-bodied participants walking with the IHK in a hip prosthesis simulator. Hip and knee joint angles and pelvic tilt angles were recorded, gait characteristics were analyzed using video recordings. Testing showed that the participants were able to walk using the IHK, and data showed that participants used different walking strategies. Points of improvement were identified for future development of the thigh unit, including completion of a synergistic gait control system, improved battery holding mechanism, and amputee user testing.