Sr. Principal C#/.NET Engineer

AllSTEM Connections; Westford (MA); On-site; USD 120,000 - 160,000; Full time

Job summary

AllSTEM Connections is seeking a seasoned Sr. Principal C#/.NET Engineer to lead the enhancement of a mission-critical security integration platform. In this role, you will tackle architectural challenges and ensure high reliability of the system. The ideal candidate will possess expert-level C# capabilities and 7–10 years of backend software engineering experience.

This position offers a chance to work with advanced technologies and to mentor junior engineers as part of a dynamic team. Apply today to make an impact in security integration!

Qualifications

• 7-10 years of professional software engineering experience focused on backend systems.
• Proven ability to work independently in a contract environment.
• Strong experience leveraging AI for development acceleration.

Responsibilities

• Design, implement, and optimize high-performance C# services.
• Lead architectural improvements for legacy components.
• Troubleshoot and resolve deep-level bugs across the system.
• Author technical documentation for complex APIs.
• Provide mentorship to mid-level engineers.

Skills

Expert-level C#

Multi-threaded programming

Networking protocols

AI Integration

Education

Bachelor's or Master's in Computer Science or related

Tools

SQL Server

Azure DevOps

GitHub Actions

ADO.NET

Entity Framework

Job description

Sr. Principal C#/.NET Engineer (Mission-Critical Systems)

We are seeking a seasoned Sr. Principal C#/.NET Engineer to lead the modernization and enhancement of a large-scale, mission-critical security integration platform. This is a high-impact technical role for a "heavy hitter" who thrives on solving deep architectural challenges and debugging complex, distributed systems. You will be responsible for accelerating the delivery of high-priority features while ensuring the platform remains highly reliable and fault-tolerant. The ideal candidate can jump into a massive, existing codebase and become productive almost immediately.

Key Responsibilities

• Design, implement, and optimize high-performance C# services and frameworks for a large-scale security ecosystem.
• Lead refactoring efforts and architectural improvements to modernize legacy components while maintaining system integrity.
• Troubleshoot and resolve deep-level bugs, memory bottlenecks, and reliability issues across multi-threaded and event-driven systems.
• Work extensively with message-based architectures, Windows services, and real-time communication protocols (Sockets, Networking).
• Author clear technical documentation for complex APIs, system interfaces, and deployment processes to ensure long-term maintainability.
• Serve as a technical authority within the engineering team, providing guidance and mentorship to mid-level and senior engineers.

Qualifications & Requirements

• Education: Bachelor's or Master's in Computer Science or a related technical field.
• Experience: 7–10 years of professional software engineering with a focus on backend systems.
• Technical Mastery
  • Expert-level C#: Deep knowledge of the .NET ecosystem (Framework and Core).
  • System Internals: Strong experience in multi-threaded programming and Windows system-level services.
  • Real-Time Communications: Proficiency in networking protocols, sockets, and message-based architectures.
  • AI Integration: Experience leveraging Copilot AI and various LLM models to accelerate development.
• Attributes: Proven ability to work independently in a contract environment with minimal ramp-up time and a "solution-first" mindset.

Preferred Credentials

• Prior experience with Security Integration or Access Control platforms.
• Advanced diagnostic skills: Windows Memory Dump analysis, memory profiling, and performance tuning.
• Database expertise: SQL Server, ADO.NET, and Entity Framework.
• Modern DevOps fluency: Azure DevOps, GitHub Actions, and CI/CD pipeline management.

Equal Opportunity Employer / Disabled / Protected Veterans