A functional index weights constituents by their role in a supply chain rather than by market capitalization. Traditional semiconductor ETFs like SMH and SOXX weight by market cap, which means NVIDIA alone can represent 20–25% of the index. This creates concentration risk and misses critical but smaller companies in the supply chain — testing equipment makers, specialty materials suppliers, packaging companies — that may offer better risk-adjusted returns.
Closelook's functional indexing approach assigns weights based on supply chain function: design, equipment, materials, fabrication, memory, packaging, testing, networking, and software. Each function receives a weight proportional to its structural importance and bottleneck potential rather than its current market valuation. This methodology surfaces companies like Advantest (testing), Resonac (materials), and ASM International (deposition equipment) that are structurally critical but underrepresented in market-cap-weighted indices. The Rubin Build-Out 100 and Euro-AI Sovereign 50 both use functional weighting.
Traditional semiconductor indices like SMH and SOXX are weighted by market capitalization, which means NVIDIA, Broadcom, and TSMC dominate while critical supply chain companies are invisible. A cap-weighted index tells you nothing about structural dynamics — it just mirrors whoever is biggest. Functional indices solve this by weighting companies by their role in the supply chain.
Closelook's Rubin Build-Out 100 and Euro-AI Sovereign 50 are functional indices that expose the real bottlenecks and dependencies in AI infrastructure. When packaging capacity constrains GPU output, a functional index surfaces the constraint companies (Amkor, ASE, TSMC packaging division) that a cap-weighted index buries. This structural lens reveals investment opportunities that traditional index construction systematically misses.
Functional indices underpin the Semiconductor ETF Problem thesis, the 6-Layer Model, and Closelook's proprietary indices including the Rubin 100 and Euro-AI Sovereign 50.
