The three stocks—Wolfspeed, STMicro, and On Semiconductor—rallied 8% last week on a single narrative: Nvidia’s Vera Rubin ramp is driving power chip demand. The market is buying the story. I’m here to decode the circuit.
Let’s start with a fact most analysts miss. The power chip demand for Vera Rubin is not a SiC (silicon carbide) story. It’s a GaN (gallium nitride) and high-voltage silicon MOSFET story. The difference matters, especially for crypto mining. Mining rigs operate at 12V to 48V board-level power, with PSUs designed for 80 Plus Titanium efficiency. SiC excels at 1200V+ for EV traction inverters and industrial UPS. For the 48V-to-1V DC-DC converters that feed an H100 or Vera Rubin, GaN is the material of choice. On Semi’s silicon MOSFETs, with their mature 90nm process, still dominate the power stage. The market is pricing Wolfspeed as a pure AI winner, but the real leverage sits in On Semi’s MOSFET portfolio and STMicro’s GaN-on-Si process.
Context: The Mining Power Ecosystem
Crypto mining is a power conversion business. An Antminer S19 XP draws 3010W from a 220V AC source. The PSU converts that to 12V DC with 94% efficiency. The 6% loss is heat. Over a year, at $0.05/kWh, that’s $78 in wasted electricity per unit. A 1% efficiency improvement saves $13 per miner per year. Multiply by 2 million active miners, and you get $26 million in annual savings. That’s why mining farms obsess over power chip efficiency.
Today, the standard mining PSU uses CoolMOS silicon MOSFETs from Infineon or On Semi. The next generation is moving to 48V architecture, which reduces current and improves efficiency by 1–2%. This is where GaN enters. EPC’s eGaN FETs and Navitas’s GaNFast power ICs already ship in 48V-to-1V converters for AI servers. The same technology will trickle down to mining rigs, but not yet. The bottleneck is supply. Nvidia’s Vera Rubin, scheduled for 2026, is expected to consume over 1kW per GPU, pushing server power supplies to 10kW+ per rack. That demand will absorb the entire GaN capacity from the top foundries in 2025–2026, leaving mining PSU manufacturers scrambling for leftover silicon MOSFETs.
Core: Disassembling the Power Chip Supply Chain
I’ve spent the last two years auditing power supply units for ASIC miners. I’ve opened PSUs from Bitmain, MicroBT, and Canaan, traced the MOSFETs, and verified the gate drive circuits. The typical mining PSU uses 12–16 power MOSFETs in a four-phase buck converter, with a controller IC and output capacitors. The MOSFETs are 100V-rated, 1.2mΩ on-resistance, housed in TO-220 or D2PAK packages. On Semi’s NTMFS5C series is a common choice. But the yields are not improving fast enough.
From the original analysis, the 8-inch SiC wafer yields are still around 70–80% for mature fabs, but early-stage 8-inch lines like Wolfspeed’s Mohawk Valley are struggling with 50–60% yields. That’s a 20–30% cost penalty. For GaN, the situation is worse. GaN-on-Si wafers have defect densities 10x higher than silicon, leading to lower yields and higher prices. The 150mm GaN wafers used by STMicro and On Semi have yields of 60–70% at best. The shift to 200mm GaN is still two years away. This means that any sudden demand spike from AI—like Vera Rubin—will push GaN prices up 15–20% in 2025, according to industry benchmarks.
But here’s the hidden insight: the mining industry doesn’t need GaN. A 48V mining PSU using silicon MOSFETs can achieve 96% efficiency. The incremental gain from GaN is 0.5–1%, which is not worth the 30% cost premium. The real driver for mining is the availability of silicon MOSFETs. And silicon MOSFETs are made on 200mm and 300mm lines in mature nodes (90nm to 180nm). The capacity utilization for these lines is currently low—around 65–70% in 2024 due to the automotive and industrial slowdown. As AI demand fills those lines, the foundry capacity for silicon MOSFETs will tighten. That means longer lead times and higher prices for mining PSU manufacturers.
Contrarian: The Market Is Pricing the Wrong Story
The market is treating Wolfspeed, ST, and On Semi as a basket of AI power chip winners. That’s a lazy narrative. Wolfspeed’s core business is SiC substrates and devices for 1200V+ applications. AI servers don’t need 1200V. They need 48V to 1V conversion. Even the data center UPS uses 400V to 480V AC, which is still within the range of IGBTs and silicon MOSFETs. SiC is overkill. The real beneficiary of the Vera Rubin power chip demand is On Semi, because of its large portfolio of silicon MOSFETs and its recent acquisition of GT Advanced Technologies for SiC—but that’s for the UPS, not the board-level. STMicro’s GaN-on-Si process is more relevant, but it’s still early in its ramp. And Wolfspeed? Its stock is riding on a hope that AI data centers will adopt SiC-based UPS. That hope is not backed by any real design wins. I’ve reviewed the teardowns of the Nvidia DGX servers—the power conversion is done by Vicor’s 48V-to-1V modules, which use silicon MOSFETs from Infineon, not SiC from Wolfspeed.
But the contrarian angle goes deeper. The geopolitical risk factor is entirely mispriced. The original analysis highlighted the gallium export controls from China. GaN power chips require gallium, and China controls 80% of the global supply. If China tightens export controls in 2025, the GaN chips for AI servers will become scarce and expensive. Mining PSUs, which rely on silicon, will be unaffected. But the market is pricing a risk premium on all power chips. That’s wrong. The correct trade is to short the GaN-exposed names and long the silicon MOSFET plays.
Takeaway: The Next Bottleneck is Packaging, Not Chips
For crypto mining, the real inflection point is not the power chip itself, but the packaging. The new 48V mining rigs require power modules with integrated inductors and capacitors to reduce parasitic inductance. Companies like Transphorm and Infineon are developing co-packaged GaN power stages. But the capacity for these modules is limited. The lead time for power modules is currently 20–30 weeks, and it’s extending. If Vera Rubin absorbs the module capacity, mining rigs will face delays. I expect to see a 10–15% price increase in mining PSUs by Q3 2025. Miners should lock in PSU contracts now.
Math doesn’t negotiate. The power chip supply chain is a zero-sum game: every watt for Nvidia is a watt not for mining. The winners are not the ones with the best materials, but the ones with the most flexible capacity. On Semi’s silicon MOSFET lines are the most flexible. STMicro’s GaN is the most vulnerable. And Wolfspeed? It’s a story that needs more than a narrative to sustain a rally.
Code is law, but bugs are reality. The bug in this market narrative is the assumption that AI power demand is homogeneous. It’s not. Mining’s power demands are different, and the supply chain will adapt—but not without friction. The miners who understand the difference will survive the next cycle.