Semba graduated with a bachelor's degree from Yale with a degree in biology in 1978. He got master's degree in Latin American Studies and medical degree from Stanford University in 1983. From 1984 to 1987 he resided at Johns Hopkins Hospital where he obtained M.P.H. degree from its University in 1991. after which he completed his studies in ophthalmology at Wilmer Eye Institute.
Semba began his career as a field assistant in the Division of Ornithology in Yale Peabody Museum of Natural History in 1976. That continued for two consecutive years until he became a technician at the Stanford Eye Bank a division of Stanford University Medical Center in Stanford, California. In 1984 he became a member of the American Academy of Ophthalmology and Wilmer Residents Association and from 1984 to 1985 he was an assistant resident at the Wilmer Eye Institute which was a part of Johns Hopkins University School of Medicine of which he became a full resident by 1985. Six years later he was promoted to an instructor and by 1991 had achieved an assistant professor position.
In 1992 Semba joined the World Health Organization for epidemiology and by 1994 he joined both the American Institute of Nutrition and the American Society for Clinical Nutrition. In the same period he worked as a molecular microbiologist at the same place. In 1996 he joined the Society for International Nutrition Research to which he still belongs. By 1997 he was promoted again, this time to associate professor, and by 2006 became professor in the same field. From 1999 to 2002 he served on board of directors at the Dwight Hall Center for Social Justice, a division of Yale University.
In 2002 he joined Gerontological Society of America and the same year became a part of Women's Eye Health which was a division of the Schepens Eye Research Institute and Harvard Medical School where he still works. From 2004 to 2006 he worked as a regional advisor at the Helen Keller International and by 2006 became a consultant for the United Nations World Food Programme. Ten years later he joined the American Society for Mass Spectrometry and World Human Proteome Organization, within which he still serves as a co-chair of the Human Eye Proteome Project.
Semba began public speaking on January 9, 1995, at the School of Public Health in University of Alabama, Birmingham. Nearly a month later he attended a National Conference at the American Society for Microbiology which was hosted at Washington, D.C., in which he spoke about Micronutrients, Vitamin A and Perinatal Transmission. Twenty-one days later he held a conference on HIV in women at the Philadelphia Sciences Group at the same place. From second to third May of the same year he, as a visiting professor, gave two lectures at the University of Washington on Effects of Nutritional Factors on Infection and “Vitamin A and HIV Infection. On November 7, 1995, he was invited to host a lecture at Valencia, Spain.
On March 10, 1996, he held a seminar on Eye Infections and Seasonal Eye Disorders at the Frederick Berman Memorial Seminar, and four days gave a lecture on the Role of Vitamin A in Perinatal Transmission in Atlanta, Georgia, at the Centers for Disease Control and Prevention. On April 17 he lectured at the University of Maryland on the importance of Vitamin A and eight days later gave the same lecture at the National Institutes of Health in Bethesda, Maryland. On May 16, 1996, he held a seminar at the same place on Vitamin A and HIV Infection and five days later held a committee on Vitamin A and Immune Function at the Institute of Medicine of Fort Detrick.
He continued lecturing on HIV and AIDS at the Center for Vaccine Development on May 29, with the title Vitamin A as an Immune Enhancer, and on June 26 he gave another lecture called Vitamin A and Infection, at the University of Ulster in Northern Ireland. On November 25 of the same year he gave a lecture at the School of Public Health, a division of Harvard University on Vitamin A and AIDS.
On February 24, 1997, Semba repeated his previous lecture at the Case Western Reserve University School of Medicine and on April 22 gave another at the University of Washington on Nutrition, Immunity, and Infection. On May 5, he attended a conference at the International Life Sciences Institute on nutrition and immunity under the same title as a year ago at Emory University. On August 1, he spoke at the International Congress of Nutrition in Montreal, Canada, on Micronutrients and the Pathogenesis of HIV/AIDS and on September 4, attended a conference on Global Strategies for the Prevention of HIV in Crystal City, Virginia. Before the year ended, on November 13, he spoke at Ghent, Belgium, about the transmission of HIV from mothers to infants and its possible reduction.
On March 23, 1998, Semba lectured at Tufts University on Vitamin A and HIV Infection and by May 17 was a public speaker at the International Congress of Infectious Diseases in Boston, Massachusetts. On June 24 he held a seminar at the United States National Library of Medicine in Bethesda, Maryland, on the Rise and Fall of Vitamin A and on August 8 spoke at the International Congress of Pediatrics in Amsterdam on the topic of Vitamin A, the Immune Response, and Infectious Diseases in Children. On November 10 he came to Valencia, Spain again where he lectured on Vitamin A and Breastfeeding and by December 4 held an annual meeting at the British Society of Immunology in Harrogate, England.
On January 9, 2007 Semba held the sixth Gordon Conference on carotenoids in Ventura, California under a title of Relationship of Carotenoids to Muscle Strength and Physical Performance in Older Adults. On May 8 of the same year he spoke at the seminar at the University of Washington on the Free Radical Theory of Aging and by July 11 was a public speaker at European Nutrition Congress in Paris, France. On the anniversary of September 11 attacks he held a conference on Nutrition and Aging in Little Rock, Arkansas which was the same one that he had in May of same year.
On March 18, 2008 he was explaining how does grand rounds work at the Division of Nephrology and on May 16 held an annual 25th conference at the Johns Hopkins University in Baltimore on Nutritional Blindness in Developing Countries. On November 10 Semba was a speaker at the American Heart Association in New Orleans and 12 days later spoke at the Gerontological Society of America in National Harbor, Maryland.