ULTRARAM™ is a III-V semiconductor memory technology which exploits resonant tunneling to allow ultra-low-energy memory logic switching (per unit area), whilst retaining non-volatility. Single-cell memories developed on GaAs substrates with a revised design and atomic-layer-deposition Al 2 O 3 gate dielectric demonstrate significant improvements compared to prior prototypes. Floating-gate (FG) memories with 20-μm gate length show 0/1 state contrast from 2.5-V program-read-erase-read (P/E) cycles with 500-μs pulse duration, which would scale to sub-ns switching speed at 20-nm node. Nonvolatility is confirmed by memory retention tests of 4×10 3 s with both 0 and 1 states completely invariant. Single cells demonstrate promising endurance results, undergoing 10 4 cycles without degradation. P/E cycling and disturbance tests are performed using half-voltages (±1.25 V), validating the high-density random access memory (RAM) architecture proposed previously. Finally, memory logic is retained after an equivalent of >10 5 P/E disturbances.