Good senior .NET developer interview questions test depth in C# and the runtime, modern ASP.NET Core design, data access, performance, testing and architecture judgment. Ask candidates to explain tradeoffs, not definitions, and pair the interview with a realistic coding task so you see how they actually build and debug.

A senior .NET developer is hired for judgment as much as syntax. They decide how services are structured, review other people’s code, and get called when production slows down at 2 a.m. A quiz on keywords won’t show any of that. The questions below are grouped by skill area, with notes on what strong answers include. Before the interview, a short coding simulation gives the panel real code to discuss instead of a resume to guess from.

What a senior .NET developer should bring

• Deep C# knowledge, including memory, async and generics
• Experience building and maintaining ASP.NET Core APIs and services
• Data access with Entity Framework Core and raw SQL when needed
• Testing discipline and code review habits
• Performance diagnosis in production
• Architecture judgment: when to split a service and when not to
• Mentoring and communication with product and other engineers

Senior vs. mid level .NET developer

C# and .NET runtime questions

1. How does async and await work under the hood, and what causes a deadlock when you block on async code?
2. Explain the difference between value types and reference types, and when boxing becomes a performance problem.
3. How does garbage collection work in .NET, and how would you reduce allocations in a hot path?
4. What does the volatile keyword guarantee, and why is it rarely the right tool?
5. When would you use Span of T or Memory of T?
6. How do closures capture variables in C#, and what bug can that cause in a loop?

What to listen for: clear mental models, specific examples from real code and an honest “I would measure first” when performance comes up.

ASP.NET Core and API design questions

1. Walk through the ASP.NET Core request pipeline. Where would you add cross cutting concerns like logging or authentication?
2. How do you structure dependency injection lifetimes, and what goes wrong when a scoped service is injected into a singleton?
3. How would you version a public API without breaking existing clients?
4. How do you handle configuration and secrets across environments?
5. How do you design an endpoint that must stay fast under heavy concurrent load?

Data access questions

1. When would you choose Entity Framework Core over Dapper or raw SQL?
2. How do you find and fix an N plus 1 query problem?
3. How do you manage database migrations safely in a team?
4. Explain how you would handle concurrency conflicts when two users edit the same record.

Testing and code quality questions

1. What is the difference between unit, integration and functional tests, and how do you decide what to test at each level?
2. How do you make code testable without over abstracting it?
3. What do you look for first when reviewing a pull request?
4. How have you introduced continuous integration or delivery to a team that didn’t have it?

Architecture and leadership questions

1. Tell us about a time you split a monolith or decided not to. What drove the decision?
2. How do you design for failure when your service depends on three external APIs?
3. How do you apply SOLID principles without making the codebase harder to follow?
4. Describe a production incident you led. What did you change afterward?
5. How do you bring a junior developer up to speed on a complex codebase?
6. How do you explain a technical tradeoff to a product manager who wants the feature next week?

How to assess senior .NET developers fairly

Interview questions show how a candidate talks about code. A coding task shows how they write it. The most reliable process combines both.

1. Agree with the hiring manager on the three or four skills that matter most for this role.
2. Send a timed coding simulation built on a realistic project, not a puzzle.
3. Review the submitted code by skill area, including readability and test coverage.
4. Run a live coding interview that extends the candidate’s own submission.
5. Finish with architecture and leadership questions from the lists above.

Glider AI coding environments support full project setups and can track how candidates use AI assisted coding during a task, so reviewers see what the candidate wrote and what they prompted. Plagiarism checks and identity verification confirm the work belongs to the person interviewing. For broader context, see the guide on challenges recruiters face in technical hiring.

Frequently asked questions

Hire senior .NET developers on evidence

The right questions help, but the strongest signal is watching a candidate work through real code. Use Glider AI Coding Simulations to see how senior .NET developers design, test and debug before your engineers commit time to interviews.