After school Sie began his career in 1958 with RCA Defense Electronics Division on advanced microwave solid state devices.
In 1984, Sie left the East Coast and joined Colorado's Tele-Communications Inc. (now Comcast and Liberty Media), as senior vice president in charge of strategic planning, programming, marketing, technology, and government relations.
In 1989 he submitted the first white paper on digital high-definition television to the United States Congress and the Federal Communications Commission.
[citation needed] In 1991, with the support of Tele-Communications Inc, Sie founded and was the chairman and chief executive officer of the Starz Encore Group.
He helped establish that visiting scholar program in 2000 at the University of Denver's Daniels College of Business.