This paper focuses on the critical considerations and practical challenges in gate driver design for non-isolated DC-DC converters using gallium nitride (GaN) devices. We discuss the circuit-level operation issues when driving GaN switches, and further review the advanced design techniques of the essential building blocks, including on-chip bootstrapping circuit, over-voltage protection, false-switching prevention, EMI noise suppression, and efficiency optimization by adaptive driving. Comparative feature analysis in specific performance aspects is demonstrated, aiming to provide a design reference regarding the requirements on integration feasibility, device safety, operation reliability, and loss alleviation.