Semiconductor Giant Modernizes 6 Mission-Critical Legacy Components

A global semiconductor leader, carrying decades of acquired software

The client is one of the world's largest semiconductor manufacturers: a global business whose fabs, test floors, and automation systems run continuously, and whose tolerance for downtime is measured in seconds, not hours. Anonymized here at the client's request, the company designs and builds precision hardware that the rest of the technology industry depends on.

Like most enterprises of its scale, its software estate was not built in one place or one decade. It was accumulated through years of mergers and acquisitions. Each acquired business arrived with its own toolchain, its own conventions, and its own mission-critical applications, many written in Visual Basic 6 and still wired directly into the equipment on the manufacturing floor. The result was a portfolio of high-value, high-risk components that nobody wanted to touch and nobody could afford to lose.

• Global manufacturing operations with always-on automation and test systems
• An application estate assembled across multiple acquisitions and engineering cultures
• Original authors of the legacy code long departed; institutional knowledge thin and undocumented

Six VB6 components were quietly capping the entire automation roadmap

Mounting technical debt from years of mergers and acquisitions had concentrated into six critical Visual Basic 6 components. These were not peripheral utilities. They sat on the hot path between the company's software systems and its precision hardware. As the business pushed to scale automation and throughput, those six components became the ceiling everything else hit.

The team brought us four interlocking problems:

• Automation drag. Every new automation initiative had to route through aging VB6 code that was slow to extend and fragile to change, stalling the broader roadmap.
• Scalability limits. The single-threaded, tightly coupled design could not keep pace with rising volume and the demands of a modern, service-oriented platform.
• Precision hardware communication risk. The components spoke directly to manufacturing equipment. Any behavioral drift during modernization could mean miscommunication with hardware, an unacceptable risk on a live production floor.
• Undocumented business logic. Roughly 3 million lines of accreted logic, with edge cases encoded only in the code itself. A conventional rewrite risked silently dropping behavior no one remembered was there.

The bar was unforgiving: modernize the architecture, unlock scalability, and remove the automation bottleneck, all without changing a single observable behavior at the hardware boundary. 100% functional parity was not a nice-to-have. It was the entire mandate.

Assessment-first, AI-accelerated, human-in-the-loop, delivered in phases

We did not start by writing code. We started by understanding the code that already existed. A general-purpose AI coding assistant operates at the snippet level and has no model of a twenty-year-old application; our platform is purpose-built for legacy modernization and works at the method, module, and architecture level. That distinction is what made parity achievable at this scale.

The engagement ran as a phased, turnkey modernization with four guiding principles:

• Assessment-first. Before any conversion, the Assessment Agent ingested a representative slice of the codebase and produced a technical-debt analysis, architecture-drift map, security-vulnerability mapping, and a prioritized list of modernization hotspots in days, not weeks.
• Phased by risk. We sequenced the six components by blast radius: lower-risk modules first to validate the pipeline, the hardware-adjacent components last, once the test harness had proven itself.
• AI agents plus senior engineers. A virtual team of modernization agents handled roughly 70% of the conversion. Our engineers and the client's architects carried the remaining business logic (the irreplaceable edge cases) over the finish line by hand.
• Human-in-the-loop at every gate. Nothing reached the client's repository without architect review. Every AI-generated pull request was reviewed, every behavioral assumption confirmed against a differential test before it was accepted.

"We had been quoted multi-year rewrites that all carried the same fine print: we couldn't promise the new system would behave exactly like the old one. ConvertEdge inverted that. Parity was the starting constraint, and the differential harness proved it on every commit. That is what let us put hardware-adjacent code into production without holding our breath."
Principal Software Architect, anonymized at the client's request

From comprehension to converted code to a parity-proving test harness

The deliverables fell into four categories: assessment and documentation outputs, a modern target architecture, the six converted components themselves, and the differential test harness that made 100% parity demonstrable rather than merely claimed.

Assessment & documentation outputs

.NET target architecture

The six VB6 components were mapped onto a modern, service-oriented .NET stack, decomposing the monolithic, tightly coupled originals into independently scalable services with clean REST boundaries, while preserving the exact wire-level behavior at the hardware interface.

The differential test harness

This was the keystone of the engagement. The QA Agent auto-generated unit, integration, and regression tests; our QA specialists refined them and ran them against live servers. The harness drove identical inputs through the legacy VB6 component and the new .NET service in parallel and compared every output, byte for byte. A differential check only passed when modern behavior matched legacy behavior exactly, including the hardware-protocol edge cases nobody had documented. Parity stopped being a claim and became a gate that every commit had to clear.

3 million lines migrated, 100% parity, and the timeline cut in half

The headline numbers tell the operational story, but the strategic outcome was bigger. With the six components modernized, the automation roadmap that had been blocked for years was unblocked. The new .NET services scale horizontally where the VB6 originals could not, and the team finally has documentation, an SBOM, and a regression suite for code that had been a black box since the acquisitions that brought it in.

Most importantly, none of this came at the cost of stability. Because parity was enforced on every commit, the hardware-adjacent components went to production without a single behavioral regression at the equipment boundary, exactly the risk the client had been most afraid of.

• Automation roadmap unblocked: new initiatives no longer route through fragile VB6 code
• Scalability headroom restored with concurrent, service-oriented .NET architecture
• A durable safety net: living documentation and an automated regression suite the team owns
• Zero behavioral regressions at the precision-hardware interface in production

How the phased engagement unfolded