Semler was born in Renmark, South Australia. His first work in the production industry was as a camera operator at a local television station. Later, he began making documentary and educational films for Film Australia. In the mid-1970s, he was the cinematographer for A Steam Train Passes (1974); Moving On (1974); and Let the Balloon Go (1976). In the late 1970s, he was the cinematographer for A Good Thing Going (1978). His first film was Stepping Out, in 1980. Allmovie praised his "stunning work" on the film Hoodwink (1981) with a screen play by Ken Quinnell.
Semler was the cinematographer for Mad Max 2 (1981). Semler's vast panoramic shots of the Australian Outback's deserts "...convincingly conveyed a parched, dusty, post-apocalyptic world" and led to international attention for his work. Semler also acted as cinematographer for the follow-up film to The Road Warrior, Mad Max Beyond Thunderdome (1985). Semler was also a cinematographer for the acclaimed Australian miniseries Bodyline (1984). In the late 1980s, Semler was the cinematographer for several popular films, such as Cocktail (1988) and Young Guns (1988).