We report on demonstration of GaN tunneling hot electron transistors (THETA) with dc current gain up to 14.5 in common-emitter configuration, which is highest value reported to date in GaN-based hot electron transistors. THETA is a promising candidate to obtain vertical high frequency transistors in GaN. In a THETA, an emitter-base (EB) barrier is applied to tunnel-inject hot electron beams, and a base-collector (BC) barrier filter cold electrons leak from the base [1]. Under forward operation condition emitter-base bias VEB < 0, the injected hot electrons quasi-ballistically transit the base and collector layers, and contribute to the collector current (IC). The electrons relaxed within the base due to scatterings and quantum reflections contribute to the base current (IB). When the EB junction is sufficiently biased, IC exceeds IB, resulting in a current gain. In this work, the transistors were designed to have unintentionally doped (UID) GaN/AlN emitter barrier to block low energy electrons, ultra-thin base (<10 nm) to enhance ballistic transport, and polarization-engineered BC barrier to limit leakage.