Celestial AI Software Engineer interview questions & guide 2026

The following questions are representative of the technical depth expected in our interviews. They are designed to test your practical knowledge of the tools and methodologies used in modern semiconductor design.

Verification & UVM

• "Explain the UVM phasing mechanism. How do you synchronize sequences with the DUT reset?"
• "How would you model a scoreboard for a protocol that supports out-of-order transactions?"
• "What is the difference between new() and create() in UVM, and why does it matter?"

These questions are based on real interview experiences from candidates who interviewed at this company. You can practice answering them interactively on Dataford to better prepare for your interview.

Preparing for an interview at Celestial AI requires a shift in mindset from pure software to hardware-software co-design. You will be evaluated not just on your coding ability, but on your understanding of the underlying engineering constraints.

Technical Proficiency & Domain Knowledge Interviews here are technically rigorous. Depending on your specific focus (Verification, CAD, or Design), you must demonstrate deep expertise in your toolset—whether that is SystemVerilog/UVM for verification, Python/Tcl/SKILL for EDA automation, or C++ for system modeling. You must show that you understand the semiconductor design lifecycle, from RTL to GDSII.

Problem-Solving in Constrained Environments We value engineers who can solve problems where the constraints are physical—thermal limits, signal integrity, and manufacturing yield. You will be asked to solve scenarios where "perfect" code is not enough; the solution must be efficient, scalable across massive clusters, and robust against the realities of silicon manufacturing.

Cross-Functional Collaboration Our technology relies on heterogeneous integration—combining photonics, electronics, and advanced packaging. You will be evaluated on your ability to communicate complex software concepts to analog designers, packaging engineers, and physicists. You must demonstrate that you can work effectively in a multidisciplinary environment where your software is a key enabler for other engineering teams.

The interview process at Celestial AI is designed to assess technical depth and your ability to thrive in a fast-paced, Series B deep-tech startup environment. The process typically begins with a recruiter screen to align on your background and interest in the semiconductor/AI space. This is followed by a technical phone screen, usually with a hiring manager or a senior engineer, focusing on the specific methodologies relevant to the role (e.g., UVM concepts for verification, scripting for CAD).

If you pass the initial screens, you will move to the onsite stage (often conducted virtually or in-person at our Santa Clara or Irvine offices). This stage consists of a panel of interviews covering technical domain knowledge, problem-solving, and behavioral fit. You should expect deep-dive questions regarding your past projects, specifically how you handled technical roadblocks in chip design or verification. The team looks for hands-on experience; they want to know how you implemented a solution, not just the theory behind it.

This timeline reflects a standard engagement for engineering roles. Note that for specialized positions like UVM Verification or CAD Engineering, the "Technical Assessment" phase often involves detailed discussions on specific industry-standard tools (like Cadence Virtuoso or Synopsys tools) rather than generic algorithmic coding tests.

Based on the technical demands of our open roles, you must be prepared to demonstrate expertise in the following areas.

Verification Methodologies (UVM & SystemVerilog)

For verification-focused software roles, this is the core evaluation area. You must demonstrate mastery of Universal Verification Methodology (UVM). We do not just look for test execution; we look for the ability to architect robust testbenches from scratch.

Be ready to go over:

• Testbench Architecture – Building UVM environments, agents, drivers, monitors, and scoreboards.

As a Software Engineer at Celestial AI, your daily work is centered on enabling the creation of the Photonic Fabric. You will often be responsible for developing and maintaining the verification infrastructure, ensuring that our complex SoCs and optical bridges are functionally correct before they go to fabrication. This involves writing extensive SystemVerilog code, creating test plans, and reviewing coverage reports to sign off on designs.

In CAD or infrastructure roles, you will own the design environment. This means you are the architect of the workflows that Analog and Digital designers use every day. You will integrate Process Design Kits (PDKs) from foundries like TSMC, write scripts to automate repetitive layout tasks, and ensure that our compute clusters are optimized for massive simulation loads. You are also responsible for data integrity, managing the version control systems that house our most valuable IP.

Collaboration is a daily necessity. You will work closely with packaging engineers to understand the physical constraints of 2.5D integration and with architects to define the requirements for the next generation of interconnects. You are expected to be proactive in identifying bottlenecks in the design flow and proposing software-driven solutions to speed up our time-to-market.

Successful candidates at Celestial AI typically possess a strong blend of software engineering skills and semiconductor industry experience.

• Technical Skills

  • Must-have: Proficiency in Python or Tcl for scripting and automation.
  • Must-have (for Verification): Expert-level knowledge of SystemVerilog and UVM.
  • Must-have (for CAD): Experience with EDA tools from Cadence (Virtuoso, Innovus, Xcelium) or Synopsys.
  • Nice-to-have: Experience with C++ for modeling, knowledge of CI/CD pipelines, and familiarity with job schedulers like SLURM.

• Experience Level

  • We generally look for 5-10+ years of relevant industry experience. Deep familiarity with advanced nodes (5nm/4nm) and complex heterogeneous integration is highly valued.
  • A Bachelor’s degree in EE, CS, or Computer Engineering is required, though a Master’s or PhD is preferred for many of our specialized roles.

• Soft Skills

  • Strong analytical and debugging skills are non-negotiable.
  • Ability to work in a "startup mode"—high ownership, ability to navigate ambiguity, and a drive to deliver results without hand-holding.

Q: Do I need a background in photonics to apply? While familiarity with photonics is a plus, it is not a strict requirement for most software/verification roles. However, you must be willing to learn the system-level concepts of our Photonic Fabric to understand what you are building and testing.

Q: What is the work culture like at Celestial AI? We are an early-stage but rapidly growing startup. The culture is collaborative, fast-paced, and technically demanding. We value "smart and dedicated people" who are self-starters. Expect a high-bandwidth environment where you have significant autonomy and responsibility.

Q: Is this a remote role?

Due to the hardware-centric nature of our work, enabling close collaboration with design and lab teams, our engineering roles are predominantly onsite in Santa Clara, CA, or Irvine, CA.

Q: What is the typical interview timeline? The process can move quickly for strong candidates. From the initial recruiter screen to the final offer, the timeline can be as short as 2-3 weeks, depending on scheduling alignment.

Q: How does Celestial AI handle compensation? We offer a competitive total compensation package that includes base salary, a bonus, and significant early-stage equity. We view every hire as a partner in our long-term success.

Know the "Memory Wall": Before your interview, ensure you understand the industry problem we are solving. Read up on why data center infrastructure is shifting from Systems-on-Chip (SoCs) to Systems of Chips, and how optical interconnects address bandwidth and latency bottlenecks.

Brush up on Industry Standards: Depending on your role, be fluent in the standards relevant to our work, such as PCIe, CXL, UCIe, or IEEE 1687 (IJTAG). Mentioning your experience with these specific protocols shows you can hit the ground running.

Prepare for Whiteboard Scripting: You may be asked to write pseudocode or actual script logic on a whiteboard (or virtual equivalent). Don't just memorize syntax; focus on showing how you structure your code for maintainability and error handling, which is crucial for our internal tools.

Joining Celestial AI as a Software Engineer means positioning yourself at the forefront of the Generative AI hardware revolution. You are not just writing code; you are enabling the Photonic Fabric™, a technology that is critical for the future of high-performance computing. The work is challenging, requiring a deep understanding of both software methodologies and silicon constraints, but the impact of your work will be felt across the entire data center industry.

To succeed, focus your preparation on your core technical domain—whether that is UVM verification, EDA automation, or SoC integration. Be ready to discuss how you solve complex, constrained problems and how you collaborate in a multidisciplinary hardware environment. We are looking for engineers who are ready to own their domain and drive innovation.

The salary data above reflects the base salary ranges for engineering roles in our California locations. Actual offers will vary based on your experience, interview performance, and the specific scope of the role. In addition to base salary, our compensation package includes bonuses and generous early-stage equity, aligning your success with the company's growth.

For further insights and to track new interview experiences, visit Dataford. Good luck with your preparation—we look forward to seeing what you can build with us.