A new proprietary Monte-Carlo simulation code dedicated to the heavy-ion cross-section prediction has been developed. The code is based on diffusion-collection equations taking into account recombination processes, considering an improved drain strike model, and new upset analysis algorithms for different circuit architectures. Simulated cross-sections are compared to heavy ion experimental characterizations for commercial bulk 65 nm single- and dual-port SRAMs. Simulation capabilities of much more complex circuits are demonstrated considering a 65 nm radiation-hardened-by-design Flip-Flop (FF).