This paper presents a family of merged-two-stage resonant-switched-capacitor boost converters with a Linear Extendable Group Operated Boost (LEGO-Boost) architecture. In the LEGO-Boost architecture, multiple resonant voltage doubler units are connected in parallel to interface with a high current input source; multiple switched-capacitor units are connected in series to interface with a high voltage output load. The operation of the resonant voltage doubler units and the switched-capacitor units are merged to create mutual advantages: the resonant voltage doubler units are used as current sources to soft-charge the series stacked switched-capacitor units and maintain voltage balancing; the stacked switched-capacitor units are used to multiply the voltage without charge sharing loss and switching loss (achieving soft-switching and soft-charging). All active switches in the LEGO-Boost architecture are configured as ground referenced half-bridge circuits. It offers advantages of high reliability, high scalability and low cost for applications such as grid-interface photovoltaic and fuel cell systems. The effectiveness of the LEGO-Boost architecture is verified by a 20 V-to-240 V 535 W (1:12 voltage conversion ratio) prototype with 94.2% peak efficiency and over 215 W/in3 power density.