The power loss due to mismatch effect among interconnected photovoltaic (PV) modules can be significantly reduced by applying the maximum power point tracking to fine granularity level. In this paper, a novel configuration is proposed to utilize a sub-module integrated converter (subMIC) for effective solar energy harvesting. Gallium Nitride (GaN) field-effect transistors (FETs) are used to construct the power circuits for high conversion efficiency and high power density. The detailed mathematical analysis is presented to provide insight into the architecture. Simulation is carried out to demonstrate the system behavior in response to real-world atmospheric conditions. The hardware prototype consisting of three subMICs is developed utilizing GaN FET as the power switches, which are based on industrial standard and are compact to fit into the junction box of commercial PV modules. The advantages in terms of conversion efficiency, system cost, and dynamic performance are experimentally proved by the comparison with a benchmark system.