Early work
Semple's writing career started in 1951, as a short story contributor to magazines such as The Saturday Evening Post and Collier's Weekly. Semple also tried writing for the theatre and had a play produced on Broadway, Tonight in Samarkand (1955), a melodrama adapted from the French.
He wrote an episode for The Alcoa Hour called "Archangel Harrigan" (1955).
He wrote another play, Golden Fleecing, which was filmed for Matinee Theatre in 1958 and premiered on Broadway in 1959.
Semple wrote "China Boy" for the TV series Buckskin (1958), "Four Against Three Millions" and "Money Go Round" for Target (1958), and "Epitaph for a Golden Girl" for Pursuit (1958). "Golden Fleecing" was bought by Metro-Goldwyn-Mayer and produced under the title The Honeymoon Machine (1961), starring Steve McQueen, following which Semple relocated to Hollywood and established himself as a writer for several television shows, including Kraft Suspense Theatre ("Knight's Gambit" 1964), Breaking Point ("Never Trouble Trouble Till Trouble Troubles You" 1964), The Rogues ("Death of a Fleming " 1964), Theatre of Stars ("The Fliers" 1965), Burke's Law (several episodes).