[3] Semmler taught English and Latin at Unley High School, South Australia until 1942, when he joined the Australian Broadcasting Commission (ABC).

He "helped launch ABC television" to which he introduced "famous programs" such as Four Corners, The Critics and Six O'Clock Rock.

[8] Other books from Semmler in this period included studies of Barcroft Boake (1965), Kenneth Slessor (1966) and Douglas Stewart (1974).

After Semmler's departure from the ABC, he worked as a book reviewer for The Sydney Morning Herald for many years.

[9] He moved to Bowral in the Southern Highlands of New South Wales,[10] where he remained busy writing books, articles and letters to the editor and presenting a "regular jazz program on the local community FM station".

[11][12] Books written and edited in this period included The ABC: Aunt Sally and Sacred Cow (1981), The War Diaries of Kenneth Slessor (1985), and his memoirs, Pictures on the Margin (1991).