Moving to modern .NET can help, but the path is rarely a one-click conversion. Dependencies, APIs, hosting, data access, authentication, and user workflows all need review. In particular, older ASP.NET applications can require substantial manual work when moving to ASP.NET Core, as Microsoft’s migration guidance explains.

The companies below offer different types of .NET and application modernization support. This is a shortlist to consider, not a scored ranking. The right choice depends on your codebase, business constraints, and whether you need a focused migration or a larger cloud transformation.

What should a .NET modernization proposal include?

The first deliverable should be a clear inventory of projects, libraries, integrations, infrastructure, and unsupported dependencies. Ask the provider to identify which components can be upgraded directly, which need refactoring, and which may need to remain on .NET Framework for now.

A useful proposal should also cover:

Compatibility checks for third-party libraries and Windows-specific APIs.
A plan for database access, authentication, and external integrations.
Automated tests for critical business behavior before code changes begin.
A deployment approach that keeps the current system available during transition.
Performance, security, and functional checks after each migration stage.

Avoid assuming that every application needs to be rewritten. An incremental route can preserve working business logic while addressing the parts that cause the most maintenance pain.

1. ModLogix — specialist in legacy Microsoft applications

ModLogix focuses on modernizing software already in use. Its .NET services cover migration from .NET Framework to modern .NET, ASP.NET application updates, architecture changes, integrations, and related assessments. The company also publishes case studies on migrating older enterprise applications and has experience with Visual Basic, Visual FoxPro, and other legacy Microsoft technologies.

Consider it for: A business-critical .NET application where preserving existing behavior and migrating in stages are essential.

Ask about: How the team will discover undocumented business rules and test them before changing the application’s runtime or architecture.

2. ScienceSoft — .NET development and application evolution

ScienceSoft offers .NET development, consulting, migration, and modernization services. Its public case studies include refactoring and migration work involving older .NET applications and business software.

Consider it for: An application that needs a mix of code modernization, integration, cloud planning, and ongoing support.

Ask about: Which parts of the system can be retained and how the proposed testing plan will protect existing functions.

3. Itransition — modernization alongside broader development

Itransition provides .NET development services that include migration and modernization. It also offers wider application engineering, integration, and testing services, which can matter when a .NET upgrade is only one part of the project.

Consider it for: A company that needs to modernize a .NET application while adding features or connecting it to other systems.

Ask about: How the migration work will be sequenced alongside product changes to limit release risk.

4. SoftServe — cloud-focused modernization

SoftServe offers cloud migration and modernization services and explicitly includes .NET workloads in its modernization offering. Its approach may fit an organization whose application upgrade is tied to a broader change in hosting, operations, or cloud architecture.

Consider it for: A .NET estate that needs cloud migration as well as application changes.

Ask about: Which proposed improvements depend on moving to the cloud and which can deliver value before that move.

5. EPAM — enterprise modernization at scale

EPAM offers modernization services covering assessment, application planning, migration, testing, and managed operations. Its cloud modernization work includes complex application estates where .NET is one of several technologies involved.

Consider it for: A large portfolio with multiple teams, environments, and dependencies to coordinate.

Ask about: How applications will be prioritized and what evidence will be used to choose between rehosting, refactoring, and rebuilding.

Run a small technical assessment before choosing

Give each shortlisted provider the same representative sample: one application, its dependency list, a diagram of connected systems, and a set of critical user journeys. Request a brief assessment of migration blockers, delivery stages, testing, rollback, and support responsibilities.

Look closely at how candidates describe unknowns. A trustworthy plan will identify the libraries or integrations that need investigation and avoid claiming that automated conversion will solve every issue. It should explain how functionality will be verified with actual users and real workloads, not just whether the code compiles.

For a larger estate, a pilot application can establish a repeatable process. Choose one with meaningful dependencies but manageable risk. Record how long discovery, migration, testing, and release take before applying the approach across the portfolio.

Final thoughts

Successful .NET modernization begins with understanding the current application and the business work it supports. Choose a partner that can show what should change now, what can wait, and how each stage will be validated. That makes the transition easier to govern and gives the team a more dependable foundation for future development.

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