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About CoolSem Technologies

Who we are CoolSem was founded in 2025 with the mission to remove one of the biggest bottlenecks in high-performance semiconductors: self-heating. By enabling far more effective cooling, we increase device output power, improve efficiency and reduce system-level overhead. The company is built on a patented technology platform, called WaLTIS, and an experienced founder team covering all aspects of the business. The WaLTIS innovation At the core of our approach is WaLTIS — the Wafer-Level Thermal Interface Stack. WaLTIS is applied directly to the bare device after full substrate removal by epitaxial lift-off. This creates a unique thermal pathway that improves heat transfer from the device to the heatsink by a factor of 15 compared with conventional packaging. WaLTIS is distinctive because it addresses all the critical physical requirements in a single stack: mechanical support, high thermal conductivity (≈250 W/m·K), RF isolation, and management of the thermal expansion mismatch between chip and heatsink. The result is that devices can be mounted directly on standard copper heatsinks, eliminating the need for low-conductivity composites such as CuMo or CuW. Compatibility with established joining techniques such as Au/Sn soldering or Ag sintering ensures straightforward adoption. Benefits for device makers This architecture delivers higher performance, longer device lifetimes, and lower cost per chip, thanks to wafer-level processing. By doubling the thermal conductivity of the heatsink and multiplying the chip-to-heatsink conductivity with a factor of 15, WaLTIS opens a new performance window that other solutions cannot match. Competing approaches are either prohibitively expensive (e.g. diamond) or significantly less effective (e.g. phase-change materials).

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