Z-source inverter (ZSI) is recently proposed as a single-stage power conversion topology. It adds voltage boost capability for complementing the usual voltage buck operation of the traditional voltage source inverter with enhanced reliability. However, its boosting capability could be limited, and therefore, it may not be suitable for some applications requiring very high voltage boost. To enhance the boosting capability, this paper proposes a new modulation technique to control the generation of the shoot-through intervals in the Z-source inverters. The proposed modulation technique achieves reliable high voltage gain operation without adding any extra hardware to the ZSI structure which preserves its single stage nature. The proposed modulation technique is analyzed in details and its performance is validated using both simulation and experimentations.