Proposed is a modified single-ended primary inductance converter (SEPIC) as a highly efficient step-up and step-down converter in continuous conduction mode. It consists of the original SEPIC components plus an auxiliary diode and switch which form a new direct power delivery path between input and output. By shortening the time period for the original SEPIC operation and increasing the time period for the direct power link operation, this converter can reduce the ripple currents and switching voltages of switches, diodes, and inductors. To verify the effectiveness of the proposed converter, experimental waveforms are given and compared with those of the original SEPIC. Under wide load variation, the average power conversion efficiency of the proposed converter was 4.9% greater than that of the original SEPIC.