Senior Software Engineer C# / .NET (m/w/d)

New Monday GmbH; Mannheim; Hybrid; EUR 70,000 - 110,000; Full time

Job summary

New Monday GmbH in Mannheim seeks a Senior Software Engineer C# / .NET (m/w/d) to design, build and maintain distributed software where performance and reliability matter. You will collaborate with product owners, architects and cross-functional teams to translate requirements into robust technical solutions.

The role emphasizes TDD, automated testing, and mentoring junior developers in a hybrid setup with on-site and remote work. English is required, German a plus.

Qualifications

• Deep, hands-on knowledge of C# 14 and modern .NET.
• Several years of experience with multi-threaded programming.
• Several years of experience with high-volume in-memory data processing.
• Solid experience designing and implementing RESTful APIs.
• Strong command of OOP, SOLID, Clean Code, multi-layer architecture and TDD.
• Practical experience with automated testing: unit tests, component tests, mocking.
• Good working knowledge of UML.
• Proven experience in hardware-related software development.

Responsibilities

• Design, develop, test and maintain scalable applications in C# and the .NET ecosystem.
• Write clean, well-documented code following Clean Architecture and the team’s coding standards.
• Work test-driven (TDD) and strengthen a culture of automated testing.
• Build robust multi-threaded solutions using locking, interlocking and parallelism in .NET.
• Turn business requirements into technical solutions together with product owners, architects and cross-functional teams.
• Review code and give constructive feedback to keep quality and consistency high.
• Mentor junior and mid-level developers and provide technical guidance.
• Identify and drive improvements in architecture, performance, reliability and maintainability.
• Troubleshoot and resolve complex issues across a distributed software stack.
• Contribute to CI/CD and modern delivery practices.

Skills

C# 14 and modern .NET

Multithreaded programming

In-memory data processing

RESTful APIs

OOP, SOLID, Clean Code

TDD / automated testing

UML

Hardware-related software development

Education

Degree in Computer Science, Software Engineering, Physics or related field

Job description

About this role

For our client, a global leader in metrology and process control for semiconductor manufacturing, we are looking for a Senior Software Engineer C# / .NET (m/w/d) for a permanent position.

The team is based in Mannheim and has more than 25 years of experience building high-precision measurement systems. Their software looks down to the atomic level and turns what it sees into actionable data for the production of the world’s most advanced computer chips.

In this role you will design, build and maintain distributed software where performance, concurrency and reliability matter. You will also help shape how the team builds that software.

At a glance

• Start: ASAP or by agreement

• Contract: Contract, full-time

• Setup: Hybrid, 3 days remote and 2 days on-site in Mannheim

• Working language: English (German is a plus)

Your tasks

• Design, develop, test and maintain scalable applications in C# and the .NET ecosystem

• Write clean, well-documented code following Clean Architecture and the team’s coding standards

• Work test-driven (TDD) and strengthen a culture of automated testing

• Build robust multi-threaded solutions using locking, interlocking and parallelism in .NET

• Turn business requirements into technical solutions together with product owners, architects and cross-functional teams

• Review code and give constructive feedback to keep quality and consistency high

• Mentor junior and mid-level developers and provide technical guidance

• Identify and drive improvements in architecture, performance, reliability and maintainability

• Troubleshoot and resolve complex issues across a distributed software stack

• Contribute to CI/CD and modern delivery practices

Your profile

Must have

• Deep, hands-on knowledge of C# 14 and modern .NET

• Several years of experience with multi-threaded programming

• Several years of experience with high-volume in-memory data processing

• Solid experience designing and implementing RESTful APIs

• Strong command of OOP, SOLID, Clean Code, multi-layer architecture and TDD

• Practical experience with automated testing: unit tests, component tests, mocking

• Good working knowledge of UML

• Proven experience in hardware-related software development

• Degree in Computer Science, Software Engineering, Physics or a related field

• Excellent English; you work well in international, cross-functional teams

Nice to have

• Real-time systems, hardware integration or optical sensor data processing (strong plus)

• Legacy modernization, such as migrating a monolith to distributed, service-oriented systems or microservices

• Distributed system design: event-based and object-based architecture, fault detection, causality methods, fault tolerance

• Relational database design

• Front-end development with .NET MAUI

• German language skills

What we offer

• A contract position at a global technology leader in a growing industry

• Technically demanding work at the intersection of software, hardware and physics

• A hybrid setup with 3 days remote per week

• An international team that values clean engineering and code quality

• Real influence on architecture, and the chance to mentor other developers

• Personal support from us throughout the hiring process