NuAxiSemiconductor trade intelligence

Same fab, different paths: Kioxia and Sandisk diverge on HBF

What happened

NAND fab joint-venture partners Kioxia and Sandisk hold differing views on the SK Hynix-led High-Bandwidth Flash (HBF) initiative: Sandisk supports it while Kioxia so far is neutral and is staking out an alternative architectural position. The HBF concept is similar to HBM, vertically stacking multiple layers of 3D NAND dies (8-high or 16-high configurations in the first HBF spec) interconnected via TSVs and microbumps to a base interposer logic die, connecting in parallel to a host GPU; standard NAND dies generally cannot be used as-is for HBF because they lack TSV keep-out zones, through-die pathways and the higher internal parallelism. Sandisk and SK Hynix launched the HBF Spec Standardization Consortium and a dedicated workstream under the Open Compute Project (OCP) in February 2026 and are the main contributors to the first open technical specification, which covers NAND die stacks (8-high/16-high, up to 512 GB), bandwidth grades (~0.4–3.0 TB/s), UCIe interconnect, packaging, reliability and software guidance; the spec was released via OCP in early August 2026, and Google and Tenstorrent then joined as consortium members. In January, HBF evangelist Professor Kim Jung-ho of KAIST said: “Samsung Electronics and Sandisk plan to integrate HBF into products from Nvidia, AMD, and Google by late next year or early 2028.” In October Sandisk said: “HBF reached a milestone in FQ1 with tape-out of our first HBF memory die; samples of our first HBF-based products remain on track for next calendar year.” Kioxia has not joined the HBF consortium; its own developments include the Optane-class GP Series SSD using gen 3 XL-FLASH with >20 million IOPS 512-byte random read performance, liquid-cooled NX1 Series E1.S NVMe SSDs for data centers and a liquid-cooled version of its PCIe gen 5 CM9 datacenter SSD, plans (per Japan's Nikkei) to use fast NAND as a DRAM alternative via a CXL module reducing data-read latency to less than one-tenth that of conventional NAND products, and an August 2025 prototype large-capacity high-bandwidth flash module with 5 TB capacity and 64 GB/s bandwidth for edge servers (not data center GPU servers), using daisy-chained serial connections of flash "beads" (not stacked layers) with 128 Gbps transceivers and differential serial signalling rather than the parallel signalling of SK Hynix/Sandisk HBF. SK Group Chairman Chey Tae-won suggested in September that an SK Hynix partnership with Kioxia could be interesting; as background, SK Hynix is a Kioxia investor through convertible bonds that could be converted into a 14.19 percent voting share holding (which would be the largest single voting share holding), and Kioxia also uses SK Hynix DRAM in some of its SSDs. Kioxia CEO Hiroo Ota opposed the idea, telling The Japan Times: “We can't just say, 'Well then, let's make it three companies,'” … “We have no idea what prompted (Chey) to say what he did.” A TrendForce April 2026 document, citing ETNews, said sources indicate the company (Sandisk) has begun engaging materials, components, and equipment partners to build an ecosystem for an HBF prototype production line, aiming to introduce prototypes in the second half of this year, with Japan a leading candidate for the production site; the industry expects the pilot production line to be completed in the second half and begin operation around year-end, with commercialization targeted for 2027 — suggesting Sandisk may be considering owning and operating its own NAND fab for HBF NAND separate from its Kioxia JV.