Cluster formations are important measures for strengthening local high-tech clusters are created and grown, especially focusing on spin-offs created by serial entrepreneurs. This study uses the software industry in Austin, Texas, USA, as its research setting, which is a rapidly growing IT cluster. During the development, a nexus of spin-offs has seen over 15 years from a single company, Tivoli Systems. According to data analysis on the spinoff founders' careers, ten serial entrepreners are identified. They tend to have careers spanning across traditional boundaries and share their experiences with novice entrepreneurs willingly. This survey finds that spin-offs founded by serial entrepreneurs facilitate cluster formations and achieve high performance, and elucidates the causes behind these phenomena.