Semler gained his training as a camera operator at a local TV station in his native Australia. Within months, he had begun to work as a cameraman, shooting news stories for the station, which, in turn, led to a nine-year stint at Film Australia. Not only did Semler work as a documentary filmmaker but he also shot anthropological films for educational and research purposes.
Semler shot his first film, Chris Noonan's "Stepping Out" (1980). He garnered attention in his homeland for his stunning work on "Hoodwink" (1981), which imbued the beauty of the Outback with symbolism. International attention came the same year for his kinetic depiction of arid, detritus-strewn wastelands in George Miller's "The Road Warrior". He went on to shoot the equally bleak landscape for "Mad Max Beyond Thunderdome" (1985). Semler was also responsible for the thrilling camerawork on Simon Wincer's "The Lighthorseman" (1987), the innovative look of the Australian comic Western "Bullseye" and the tension-inducing beauty of isolation of Philip Noyce's "Dead Calm" (both 1989).
Hollywood beckoned in 1988 with Roger Donaldson's pleasant but forgettable "Cocktail" and Christopher Cain's revisionist Western "Young Guns". Semler won further praise for his work on John Milius' "Farewell to the King" (1989) and garnered some of the best notices of his career and a 1990 Oscar for Best Cinematography for the stirring images (breathtaking landscapes, battle sequences and a buffalo stampede) of Kevin Costner's autumnal Western "Dances With Wolves". Subsequent work has included Ron Underwood's "City Slickers" (1991), the video game universe of "Super Mario Brothers", the cartoon-like world of "The Last Action Hero" (both 1993) and a return to the "Mad Max" post-apocalyptic look in Kevin Reynolds' "Waterworld" (1995).
Despite his big screen success, Semler has still worked on TV projects, including the Australian soap operatic miniseries "Return to Eden" (syndicated, 1984) and the Joseph Sargent- directed American TV-movie, "Passion Flower" (CBS, 1986). He has also acted as 2nd unit director on two epic miniseries: Simon Wincer's Western "Lonesome Dove" (CBS, 1989), which included numerous scenes of a cattle drive; and "Son of the Morning Star" (ABC, 1991), which recreated the Battle of Little Bighorn.