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Recently there has been renewed interest in resonant tunnel diodes (RTD) owing to the demonstration of repeatable room temperature negative differential resistance (RT-NDR) [1], [2] and high peak current densities [3] in GaN-based RTDs. While most of the successful demonstrations of RT-NDR have been from device structures grown on low dislocation-density, freestanding (FS) GaN substrates, there have been a few reports of repeatable RT-NDR from GaN-based RTDs grown on GaN templates on sapphire [4], [5], which have significantly higher densities of threading dislocations (TDs) than FS GaN substrates, but much lower cost. Furthermore, due to the large spontaneous and piezoelectric charge found at the heterointerfaces in III-nitrides, GaN-based RTDs, such as the one illustrated in Fig. 1(a), have highly unusual energy band diagrams, even at 0V bias [Fig. 1(b)]. However, observations of RT-NDR in GaN RTDs on GaN templated sapphire substrates have been restricted to devices of very small active area, typically less than 10 μm 2 [4], [5].