There is a brand new chokepoint stack hiding inside Rubin Ultra. Most of the names are micro-caps.
The 800 VDC AI rack architecture has a problem nobody is pricing. Everything between the wall and the GPU die is being rebuilt from scratch. That voltage step-down conversation sounds technical, but behind it is a brand new bottleneck stack with names most generalists have never heard of.
The step-down used to be split across multiple stages of silicon MOSFETs and SiC. At 800 V dropping to about 1 V on a 120 kW rack, that approach no longer works.
The new stack needs wide-bandgap GaN, single-chip high-voltage parts, solid-state circuit breakers, decoupling capacitors that physically fit under the die, and thermal spacers that hold up to the heat density. Each one of those is a separate company.
Power Integrations, ticker
$POWI, is the only firm in volume production with 1250V and 1700V single-chip GaN. They are in NVIDIA's 800 VDC whitepaper. Profitable. Around $4 billion MC. Of the 5 names below, this is the only one that already has scale.
Innoscience, ticker 2577 on the Hong Kong exchange, is the largest pure-play GaN IDM at about 30% global share. They own their own fabs. They are the only Chinese name on NVIDIA's 800 VDC supplier list. TSMC is shutting its GaN foundry mid-2027, which makes Innoscience structurally more important to every fabless GaN player.
Ideal Power, ticker
$IPWR, builds B-TRAN bidirectional switches positioned as the safety standard for 800 V solid-state circuit breakers. They just signed an LOI for an NVIDIA Rubin Ultra 800 VDC ecosystem prototype. They are pre-revenue and around $70 million market cap. This is a lottery ticket on whether B-TRAN becomes the de facto safety standard.
Smoltek, ticker SMOL on Nasdaq Stockholm, makes CNF-MIM under-die decoupling capacitors with about 50% higher density at 30 to 40% lower cost. The PDN, the power delivery network at the chip level, is one of the binding problems at 800 V. Smoltek is pre-revenue at around $40 to 55 million market cap.
Kostecsys, ticker 355150 on the Korean KOSDAQ, makes thermal spacers for SiC and GaN power modules. They already have a ₩59.4 billion deal with Texas Instruments. They are the least sexy and probably the most "real" of the five.
The reason this stack is worth tracking is the timing.
800 VDC racks are not a 2030 problem, but closer to a 2027 deployment. NVIDIA's Rubin Ultra reference architecture runs on 800 VDC. By the time analysts publish coverage on POWI and Innoscience, the design wins are locked. The 12 to 24 month customer qualification cycle for power semiconductors compresses the window inside which the trade exists.
Half of these names are pre-revenue, so the execution risk is real. The reason they are worth knowing is that they sit on the narrowest physical chokepoint in the entire AI rack power chain, and the chokepoint is being designed around them in real time.
(not financial advice)