This paper explores a coupled inductor based interleaved boost converter with soft-switching auxiliary circuit for high gain DC-DC application. The converter is capable of offering high gain with a flexible choice of turns ratio of the coupled inductor but simultaneously maintaining a reduced voltage stress on the main switch. Either a passive or active clamp circuit can be used to limit the switch voltage stress arising due to the leakage of the coupled inductor. The additional auxiliary zero-voltagetransition (ZVT) circuit allows the switching node current to be diverted to an auxiliary inductor and a transistor placed across the main inductor, thus ensuring zero voltage turn-on of the main switch and improved converter efficiency. The auxiliary devices operate at zero current switching and this addition has no effect on the control of the main boost circuit. A 300 W GaN based hardware prototype with input from 30 V - 40 V and 320 V output and operating at switching frequency of 200/300 kHz has been developed to validate the converter's operation in hardware.