This paper presents the analysis of a nonisolated high-voltage-gain single-switch dc-dc converter based on the integration of the boost and SEPIC topologies. The converter employs a voltage multiplier at the output of the SEPIC stage, which is connected in series with the output of the boost stage, aiming a high step-up ratio operation with limited duty cycle values. An accurate steady state analysis considering the influence of the leakage inductance of the SEPIC coupled inductor in the energy transfer process is detailed in the paper. The several theoretical results are then used to derive a design methodology for the circuit. Experimental results for a 500 W, 48 V input voltage, 400 V output voltage, 96.3% peak efficiency and 100 kHz switching frequency prototype are provided to demonstrate the feasibility of the proposed scheme and to validate the mathematical analysis carried out.