He worked in a number of research laboratories in Germany and the United States and taught electrical engineering at the University of Colorado from 1968 to 1976. He joined the UCSB faculty in 1976, focusing its semiconductor research program on the emerging compound semiconductor Technology rather than on mainstream silicon Technology.
Along with Charles Kittel he co-authored the popular textbook Thermal Physics, first published in 1980, and still used today. He is also the author of the textbook Quantum Mechanics for Engineering, Materials Science and Applied Physics.
Kroemer was elected as a member of the National Academy of Engineering in 1997 and the National Academy of Sciences in 2003. He always preferred to work on problems that are ahead of mainstream Technology. In the 1950s, he invented the drift transistor and was the first to point out that advantages could be gained in various semiconductor devices by incorporating heterojunctions. Most notably, in 1963 he proposed the concept of the double-heterostructure laser, which is now a central concept in the field of semiconductor lasers. Kroemer became an early pioneer in molecular beam epitaxy, concentrating on applying the Technology to untried new materials.