A semi-actuated above knee prosthetic system (100), includes a shank link (105) coupled to an artificial foot (108), a knee mechanism (107) connected to the shank link (105) and a thigh link (103) attached to an above-knee remaining lower limb (110) of an amputee, is operable in two modes controlled by a signal processor (130) linked to various sensors (120,122,124,126,127). In the actuated mode, power is delivered to a torque generator (104) connected to the knee mechanism (107) to move thigh (103) and shank links (105). In the un-actuated mode, a control circuit (204) operates in a non-powered manner with modulated resistance in the knee mechanism (107). Power is delivered through an electric motor (202) connected to a battery source (205) and employed to drive a hydraulic pump (201) as part of an overall hydraulic power unit (200) including the torque generator (104)
