Alpha and Omega Semiconductor v. Force MOS Technology — Court Rules ‘And’ Means ‘And’ in MOSFET Heat-Dissipation Patent

Background

Alpha and Omega Semiconductor (AOS) and Force MOS Technology are competitors in the market for metal oxide semiconductor field effect transistors — MOSFETs — the tiny switches that manage power flow in everything from phone chargers to electric vehicles. Force MOS owns three patents covering improvements to “trench” MOSFET designs, which route current vertically through etched channels in a silicon chip. The third patent at issue, U.S. Patent No. 7,646,058, aims to improve heat dissipation by specifying that both the metallic contact plugs and the front metal layer must be made of a material with thermal conductivity higher than that of aluminum or its alloys.

After Force MOS sent infringement demand letters in 2022 and 2023, AOS filed a declaratory judgment action. Force MOS counterclaimed, asserting that AOS’s products infringe all three patents. AOS moved for summary judgment on the ’058 patent, arguing that its products use tungsten contact plugs — which have lower thermal conductivity than aluminum — and therefore cannot infringe a claim requiring both components to exceed aluminum’s thermal conductivity.

The Court’s Holding

Judge Pitts granted AOS’s motion for summary judgment of noninfringement. The central dispute was whether the word “and” in claim 1 — requiring that “said metallic contact plugs and said front metal are composed of a metallic material having a thermal conductivity higher than… aluminum” — should be read conjunctively (both must exceed aluminum) or disjunctively (either one suffices).

The court held that “and” unambiguously means “and.” The opinion noted that the same claim uses “and/or” elsewhere (“aluminum and/or aluminum alloys”), which strongly implies that the standalone “and” carries a different, purely conjunctive meaning. Where prior Federal Circuit cases have read “and” as disjunctive, it was because the claim contained additional language signaling a disjunctive reading — no such language exists here.

Force MOS argued that a conjunctive reading would exclude its own preferred embodiments from the patent’s scope. The court acknowledged this but held that “courts may not redraft claims to cure a drafting error made by the patentee,” citing Lucent Technologies v. Gateway. When the claim language is unambiguous, courts must give it effect even if it excludes all disclosed embodiments.

Separately, the court granted Force MOS’s cross-motion on the marking defense, finding that AOS and its subsidiary Jireh failed to meet their initial burden under Arctic Cat v. Bombardier by not identifying specific unmarked patented products in their damages contentions or interrogatory responses.

Key Takeaways

• “And” means “and” absent strong textual signals otherwise. Patent drafters cannot rely on prosecution history or disclosed embodiments to override the plain conjunctive meaning of “and” in a claim, especially when the same claim uses “and/or” elsewhere.
• Claim language that excludes preferred embodiments is a drafting risk the patentee bears. Courts will not rewrite unambiguous claims to save the patentee from a narrow or unintended construction.
• Marking defense requires early, specific identification of unmarked products. Under Arctic Cat, an accused infringer must put the patentee on notice of specific unmarked articles — generalized assertions in interrogatory responses won’t suffice.

Why It Matters

This opinion is a practical reminder for patent drafters working in the semiconductor space — and beyond — that every word in a claim carries legal weight. The use of “and” versus “and/or” versus “or” can be outcome-determinative at summary judgment. Force MOS lost infringement coverage over its own patent’s heat-dissipation feature because it used “and” in a claim that also deployed “and/or,” locking in a conjunctive reading. For companies defending against infringement allegations, the case also underscores that marking defenses must be substantiated early in litigation through specific, well-documented contentions.