C# Developer Interview Questions - IT Hiring Guide

Introduction

Hiring the right C# Developer is critical for Information Technology teams building reliable, maintainable applications on the .NET platform. A strong C# Developer delivers clean code, scalable architecture and efficient problem-solving under real-world constraints.

This guide provides a practical set of screening-ready interview questions for hiring managers and technical teams: basic questions to verify fundamentals, intermediate prompts to assess applied skills, advanced problems for senior-level candidates, and targeted one-way video pre-screening questions to speed up and standardise early-stage evaluation.

C# Developer Interview Questions

Basic C# Developer Interview Questions

1. What are the main differences between value types and reference types in C#?
2. Explain the purpose of the using statement and when you would use it.
3. What is the difference between an interface and an abstract class?
4. Describe how exception handling works in C# and when to use try/catch/finally.
5. What is a delegate in C# and how is it typically used?
6. How does the async/await pattern improve application responsiveness?
7. Explain what LINQ is and give an example of a simple query against a collection.
8. What is the Common Language Runtime (CLR) and why is it important for .NET applications?

Intermediate C# Developer Interview Questions

1. How do you implement dependency injection in a C# application and what benefits does it provide?
2. Explain SOLID principles and give a concrete example of applying one in C# code.
3. Describe differences between Task, Thread and async/await and when to choose each approach.
4. How would you manage database access in a C# application using Entity Framework? Discuss migrations and performance considerations.
5. Explain value vs reference equality in C# and how to override Equals and GetHashCode correctly.
6. Describe how memory management and garbage collection work in .NET and how to detect memory leaks.
7. What strategies do you use for unit testing C# code and how do you mock dependencies?
8. Explain covariance and contravariance in C# generics with a use-case example.
9. How do you profile and optimize a slow C# application? List tools and typical steps.
10. Describe how you would secure sensitive configuration settings in a C# application (e.g., connection strings, API keys).

Advanced C# Developer Interview Questions

1. Design a thread-safe caching mechanism in C# for high-concurrency access and discuss eviction policies.
2. Explain the internals of the .NET garbage collector and how Server GC differs from Workstation GC.
3. How would you implement a custom awaitable type in C# and why might you do so?
4. Discuss advanced patterns for asynchronous streams (IAsyncEnumerable) and backpressure handling.
5. Describe how expression trees work and provide an example where you would build or modify one at runtime.
6. Explain memory management for large object heap (LOH) and strategies to avoid LOH fragmentation.
7. How do you analyze and fix deadlocks in a C# application? Walk through a debugging approach with examples.
8. Discuss binary serialization vs JSON serialization in .NET, performance trade-offs and versioning concerns.
9. How would you design a microservice in .NET that handles high throughput and graceful degradation?
10. Explain runtime code generation techniques in C# (Reflection.Emit or Roslyn) and safe use cases for them.

Pre-Screening Video Interview Questions for C# Developer

Use one-way video questions to quickly evaluate communication, problem-structuring and core technical understanding before scheduling live interviews. Ask candidates to record concise answers (60–180 seconds) so hiring teams can compare responses consistently.

1. Describe a recent C# project you worked on and your primary contributions.
   Evaluation: Look for clarity on responsibilities, specific technical challenges, technologies used (.NET versions, frameworks) and measurable outcomes.
2. Explain how you would handle a performance issue in a C# web API that is experiencing high latency.
   Evaluation: Expect a structured approach: profiling, identifying bottlenecks, caching/database fixes, async handling and monitoring improvements.
3. Give an example of a bug you fixed that involved multithreading or concurrency; what was the root cause and your solution?
   Evaluation: Assess understanding of race conditions, synchronization primitives used (locks, Concurrent collections) and validation of the fix.
4. How do you ensure code quality and maintainability in C#—mention tools, practices and processes you follow.
   Evaluation: Look for use of code reviews, unit/integration tests, static analysis (linters), CI pipelines and design principles like SOLID.
5. What are your strategies for staying current with C# and .NET ecosystem updates?
   Evaluation: Prefer candidates who reference continuous learning practices: reading docs, following changelogs, hands-on experimentation or contributions to projects.

Conclusion

This set of role-specific questions helps IT hiring teams evaluate C# Developer candidates across fundamentals, applied skills and advanced system design. Structured interview prompts and scenario-based problems identify practical competence and cultural fit.

ScreeningHive one-way video interviews accelerate candidate screening, standardise evaluations across hiring teams and reduce time-to-hire by letting reviewers watch consistent responses on their schedule. Use these questions to build efficient, objective C# Developer pipelines that surface the best talent quickly.