Semil founded Haystack, an early-stage investment firm now investing out of its sixth institutional fund, Haystack Ventures VI, with his colleagues Aashay Sanghvi and Divya Dhulipala. He is also a Venture Partner at Lightspeed Ventures. Prior to investing, Semil held various product and operational roles at earl-stage startups, the most recent one being acquired by Apple. In 2017, Semil was named to Midas Brink List by Forbes, and in 2022 and 2023, he was named to the Midas List for seed investors by Forbes. While working and investing, he has also been a long-time consistent writer about technology and investing at outlets such as Harvard Business Review, TechCrunch, and Quora.